Skip to main content

Full text of "Argon, a New Constituent of the Atmosphere"

See other formats

[ 187 ] 

VI. Argon, a New Constituent of the Atmosphere. 
By Lord Rayleigh, See. E.S., and Professor William Eamsay, F.RS. 

Received and Read January 31, 1895. 

"Modern discoveries have not been made by large collections of facts, with, subsequent discussion, 
separation, and resulting deduction of a truth thus rendered perceptible. A few facts have suggested an 
hypothesis, which means a supposition, proper to explain them. The necessary results of this supposition 
are worked out, and then, and not till then, other facts are examined to see if their ulterior results are 
found in Nature." — De Morgan, " A Budget of Paradoxes," ed. 1872, p. 55. 

1. Density of Nitrogen from Various Sources. 

In a former paper* it has been shown that nitrogen extracted from chemical 
compounds is about one-half per cent, lighter than " atmospheric nitrogen." 

The mean numbers for the weights of gas contained in the globe used were as 
follows :— 


From nitric oxide 2*3001 

From nitrous oxide 2*2990 

From ammonium nitrite . , . . 2*2987 

while for " atmospheric" nitrogen there was found — 

By hot copper, 1892 . . . . . 2*3103 

By hot iron, 1893. ..... 2*3100 

By ferrous hydrate, 1894 . . . 2*3102 

At the suggestion of Professor Thoepe, experiments were subsequently tried with 
nitrogen liberated from urea by the action of sodium hypobromite. The carbon and 
hydrogen of the urea are supposed to be oxidized by the reaction to C0 2 and H 3 0, 
the former of which would be retained by the large excess of alkali employed. It 
was accordingly hoped that the gas would require no further purification than drying. 
If it proved to be light, it would at any rate be free from the suspicion of containing 

* Rayleigh, "On an Anomaly encountered in Determinations of the Density of Nitrogen Gas, 
Proc. Roy. Soc.,' vol. 55, p. 340, 1894 
MDCCCXCV.— A. 2 B 2 27.6.95. 



The hypobromite was prepared from commercial materials in the proportions 
lecommended for the analysis of urea — ^100 grams, caustic soda, 250 cub. centims. 
water, and 25 cub. centims. of bromine. For our purpose about one and a half times 
the above quantities were required. The gas was liberated in a bottle of about 
900 cub. centims. capacity, in which a vacuum was first established. The full quan- 
tity of hypobromite solution was allowed to run in slowly, so that any dissolved gas 
might be at once disengaged. The urea was then fed in, at first in a dilute condition, 
but, as the pressure rose, in a 10 per cent, solution. The washing out of the 
apparatus, being effected with gas in a highly rarefied state, made but a slight 
demand upon the materials. The reaction was well under control, and the gas could 
be liberated as slowly as desired. 

In the first experiment, the gas was submitted to no other treatment than slow 
passage through potash and phosphoric anhydride, but it soon became apparent that 
the nitrogen was contaminated. The " inert and inodorous" gas attacked vigorously 
the mercury of the Topler pump, and was described as smelling like a dead rat. As 
to the weight, it proved to be in excess even of the weight of atmospheric nitrogen. 

The corrosion of the mercury and the evil smell were in great degree obviated by 
passing the gas over hot metals. For the fillings of June 6, 9, 13, the gas passed 
through a short length of tube containing copper in the form of fine wire, heated by 
a flat Bunsen burner, then through the furnace over red-hot iron, and back over 
copper oxide. On June 19 the furnace tubes were omitted, the gas being treated 
with the red-hot copper only. The results, reduced so as to correspond with those 
above quoted, were— 

June 6 2*2978 

,, *j . . . . . j . A Ziuoi 

,, J. O t » » » . . Li Zl\jO^J 

X J , , , . . , Li ZiUoQl 


Mean . . . . 2'2985 

Without using heat it has not been found possible to prevent the corrosion of the 
mercury. Even when no urea is employed, and air simply bubbled through the hypo- 
bromite solution is allowed to pass with constant shaking over mercury contained in 
a U tube, the surface of the metal was soon fouled. When hypochlorite was 
substituted for hypobromite in the last experiment there was a decided improvement, 
and it was thought desirable to try whether the gas prepared from hypochlorite and 
urea would be pure on simple desiccation. A filling on June 25 gave as the weight 
2*3343, showing an excess of 36 mgs., as compared with other chemical nitrogen, and 
of about 25 mgs. as compared with atmospheric nitrogen. A test with alkaline 
pyrogallate appeared to prove the absence from this gas of free oxygen, a,nd only a 
trace of carbon could be detected when a considerable quantity of the gas was passed 
over red-hot cupric oxide into solution of baryta. 


Although the results relating to urea nitrogen are interesting for comparison with 
that obtained from other nitrogen compounds, the original object was not attained on 
account of the necessity of retaining the treatment with hot metals. We have found, 
however, that nitrogen from ammonium nitrite may be prepared without the employ- 
ment of hot tubes, whose weight agrees with that above quoted. It is true that the 
gas smells slightly of ammonia, easily removable by sulphuric acid, and apparently 
also of oxides of nitrogen. The solution of potassium nitrite and ammonium chloride 
was heated in a water-bath, of which the temperature rose to the boiling-point only 
towards the close of operations. In the earlier stages the temperature required 
careful watching in order to prevent the decomposition taking place too rapidly. The 
gas was washed with sulphuric acid, and after passing a Nessler test, was finally 
treated with potash and phosphoric anhydride in the usual way. The following results 
have been obtained : — 

July 4 ...... . 2*2983 

«3 lO .»...,. Zj ZiijuXj 

Mean .... 2*2987 

It will be seen that in spite of the slight nitrous smell there is no appreciable differ- 
ence in the densities of gas prepared from ammonium nitrite with and without the 
treatment by hot metals. The result is interesting, as showing that the agreement 
of numbers obtained for chemical nitrogen does not depend upon the use of a red 
heat in the process of purification. 

The five results obtained in more or less distinct ways for chemical nitrogen stand 
thus :— 

From nitric oxide .............. 2*3001 

From nitrous oxide . . . . . . . . . . . . . 2*2990 

From ammonium nitrite purified at a red heat . . . . 2*2987 

Jj rom urea ................ ^'2985 

From ammonium nitrite purified in the cold . . . . . 2*2987 

These numbers, as well as those above quoted for " atmospheric nitrogen," are subject 
to a correction (additive) # of *0006 for the shrinkage of the globe when exhausted.! If 
they are then multiplied in the ratio of 2*3108 : 1*2572, they will express the weights 
of the gas in grams, per litre. Thus, as regards the mean numbers, we find as the 
weight per litre under standard conditions of chemical nitrogen 1*2511, that of 
atmospheric nitrogen being 1-2572. 

[* In the Abstract of this paper (' Proc. Roy. Soc.,' vol. 57, p. 265) the correction of '0006 was 
erroneously treated as a deduction.— April, 1895.] 

f Rayleigh, " On the Densities of the Principal Gases/' '* Proc. Roy. Soc,,' vol. 58, p. 134, 1893. 


It is of interest to compare the density of nitrogen obtained from chemical com- 
pounds with that of oxygen. We have N 2 : 2 = 2*2996 : 2*6276 = 0*87517 ; so that 
if 2 = 16, N 3 = 14*003. Thus, when the comparison is with chemical nitrogen, 
the ratio is very nearly that of 16 : 14. But if " atmospheric nitrogen" be substituted, 
the ratio of small integers is widely departed from. 

The determination by Stas of the atomic weight of nitrogen from synthesis of 
silver nitrate is probably the most trustworthy, inasmuch as the atomic weight of 
silver was determined with reference to oxygen with the greatest care, and oxygen is 
assumed to have the atomic weight 16. If, as found by Stas, AgN0 3 :Ag = 1*57490:1, 
and Ag ; : O = 107*930 : 16, then N : O = 14*049 : 16. 

To the above list may be added nitrogen, prepared in yet another manner, whose 
weight has been determined subsequently to the isolation of the new dense constituent 
of the atmosphere. In this case nitrogen was actually extracted from air by means 
of magnesium. The nitrogen thus separated was then converted into ammonia by 
action of water upon the magnesium nitride, and afterwards liberated in the free 
state by means of calcium hypochlorite. The purification was conducted in the usual 
way, and included passage over red-hot copper and copper oxide. The following was 
the result :— 

Globe empty, October 30, November 5 ." . . . . 2*82313 
Globe full, October 31 ........'. . '52395 

Weight of gas ............. 2*29918 

It differs inappreciably from, the mean of other results, viz., 2*2990, and is of 
special interest as relating to gas which, at one stage of its history, formed part of 
the atmosphere. 

Another determination with a different apparatus of the density of " chemical " 
nitrogen from the same source, magnesium nitride, which had been prepared by 
passing " atmospheric " nitrogen over ignited magnesium, may here be recorded. The 
sample differed from that previously mentioned, inasmuch as it had not been 
subjected to treatment with red-hot copper. After treating the nitride with water, 
the resulting ammonia was distilled off, and collected in hydrochloric acid ; the 
solution was evaporated to dryness ; the dry ammonium chloride was dissolved in 
water, and its concentrated solution added to a freshly prepared solution of sodium 
hypobromite. The nitrogen was collected in a gas-holder over water which had 
previously been boiled, so as at all events partially to expel air. The nitrogen passed 
into the vacuous globe through a solution of potassium hydroxide, and through two 
drying-tubes, one containing soda-lime, and the other phosphoric anhydride. 

At 18*38° C, and 754*4 mgs. pressure, 162*843 cub. centims. of this nitrogen 
weighed 0*18963 gram. Hence :— 

Weight of 1 litre at 0° C. and 760 millims. pressure . . . 1*2521 gram. 


The mean result of the weight of 1 litre of " chemical " nitrogen has been found 
to equal 1*2511, It is therefore seen that " chemical " nitrogen, derived from 
" atmospheric " nitrogen, without any exposure to red-hot copper, possesses the 
usual density. 

Experiments were also made, which had for their object to prove that the ammonia, 
produced from the magnesium nitride, is identical with ordinary ammonia, and 
contains no other compound of a basic character. For this purpose, the ammonia 
was converted into ammonium chloride, and the percentage of chlorine determined 
by titration with a solution of silver nitrate which had been standardized by titrating 
a specimen of pure sublimed ammonium chloride. The silver solution was of such a 
strength that 1 cubic centim. precipitated the chlorine from 0*001701 gram, of 
ammonium chloride. 

1. Ammonium chloride from orange-coloured sample of magnesium nitride. 
0*1106 gram, required 43*10 cub. centims. of silver nitrate = 66*35 per cent, of 


2. Ammonium chloride from blackish magnesium nitride. 

0*1118 gram, required 43*6 cub. centims. of silver nitrate = 66*35 per cent, of 

3. Ammonium chloride from nitride containing a large amount of unattacked 

0*0630 gram, required 24*55 cub. centims. of silver nitrate = 66*30 per cent, of 

Taking for the atomic weights of hydrogen, H = 1*0032, of nitrogen, N = 14*04,: 
and of chlorine, CI = 35*46, the theoretical amount of chlorine in ammonium chloride 
is 66*27 per cent. 

From these results — that nitrogen prepared from magnesium nitride obtained by 
passing "atmospheric" nitrogen over red-hot magnesium has the density of 
"chemical" nitrogen, and that ammonium chloride prepared from magnesium nitride 
contains practically the same percentage of chlorine as pure ammonium chloride — it 
may be concluded that red-hot magnesium withdraws from "atmospheric" nitrogen 
no substance other than nitrogen capable of forming a basic compound with hydrogen. 

In a subsequent part of this paper, attention will again be called to this 
statement. (See addendum p. 240.) 

2. Reasons for Suspecting a hitherto Undiscovered Constituent in Air. 

When the discrepancy of weights was first encountered, attempts were naturally 
made to explain it by contamination with known impurities. Of these the most 
likely appeared to be hydrogen, present in the lighter gas, in spite of the passage over 
red-hot cupric oxide. But, inasmuch as the intentional introduction of hydrogen 
into the heavier gas, afterwards treated in the same way with cupric oxide, had no 
effect upon its weight, this explanation had to be abandoned ; and, finally, it became 


clear that the difference could not be accounted for by the presence of any known 
impurity. At this stage it seemed not improbable that the lightness of the gas 
extracted from chemical compounds was to be explained by partial dissociation of 
nitrogen molecules N 2 into detached atoms. In order to test this suggestion, both 
kinds of gas were submitted to the action of the silent electric discharge, with the 
result that both retained their weights unaltered. This was discouraging, and a 
further experiment pointed still more markedly in the negative direction. The 
chemical behaviour of nitrogen is such as to suggest that dissociated atoms would 
possess a higher degree of activity, and that, even though they might be formed in 
the first instance, their life would probably be short. On standing, they might be 
expected to disappear, in partial analogy with the known behaviour of ozone. With 
this idea in view, a sample of chemically-prepared nitrogen was stored for eight 
months. But, at the end of this time, the density showed no sign of increase, 
remaining exactly as at first. * 

Regarding it as established that one or other of the gases must be a mixture, 
containing, as the case might be, an ingredient much heavier or much lighter than 
ordinary nitrogen, we had to consider the relative probabilities of the various possible 
interpretations. Except upon the already discredited hypothesis of dissociation, it 
was difficult to see how the gas of chemical origin could be a mixture. To suppose 
this would be to admit two kinds of nitric acid, hardly reconcilable with the work of 
Stas and others upon the atomic weight of that substance. The simplest explanation 
in many respects was to admit the existence of a second ingredient in air from which 
oxygen, moisture, and carbonic anhydride had already been removed. The pro- 
portional amount required was not great. If the density of the supposed gas were 
double that of nitrogen, one-half per cent, only by volume would be needed ; or, if the 
density were but half as much again as that of nitrogen, then one per cent, would 
still suffice. But in accepting this explanation, even provisionally, we had to face the 
improbability that a gas surrounding us on all sides, and present in enormous 
quantities, could have remained so long unsuspected. 

The method of most universal application by which to test whether a gas is pure or 
a mixture of components of different densities is that of diffusion. By this means 
Gbaham succeeded in effecting a partial separation of the nitrogen and oxygen of the 
air, in spite of the comparatively small difference of densities. If the atmosphere 
contain an unknown gas of anything like the density supposed, it should be possible 
to prove the fact by operations conducted upon air which had undergone atmolysis. 
If, for example, the parts least disposed to penetrate porous walls were retained, the 
"nitrogen" derived from it by the usual processes should be heavier than that 
derived in like manner from unprepared air. This experiment, although in view from 
the first, was not executed until a later stage of the inquiry (§ 6). when results were 

* Rayleigh, ' Proe. Roy, Soe.,' vol. 55, p. 344, 1894, 


obtained sufficient of themselves to prove that the atmosphere contains a previously 
unknown gas. 

But although the method of diffusion was capable of deciding the main, or at any 
rate the first question, it held out no prospect of isolating the new constituent of the 
atmosphere, and we therefore turned our attention in the first instance to the con- 
sideration of methods more strictly chemical. And here the question forced itself 
upon us as to what really was the evidence in favour of the prevalent doctrine that 
the inert residue from air after withdrawal of oxygen, water, and carbonic anhydride^ 
is all of one kind. 

The identification of " phlogisticated air " with the constituent of nitric acid is due 
to Cavendish, whose method consisted in operating with electric sparks upon a short 
column of gas confined with potash over mercury at the upper end of an inverted 
U-tube.* This tube (M) was only about y^- inch in diameter, and the column of 
gas was usually about 1 inch in length. After describing some preliminary trials, 
Cavendish proceeds : — " I introduced into the tube a little soap-lees (potash), and then 
let up some dephlogisticatedt and common air, mixed in the above mentioned 
proportions which rising to the top of the tube M, divided the soap-lees into its two 
legs. As fast as the air was diminished by the electric spark, I continued adding more 
of the same kind, till no further diminution took place : after which a little pure dephlo- 
gisticated air, and after that a little common air, were added, in order to see whether 
the cessation of diminution was not owing to some imperfection in the proportion of 
the two kinds of air to each other ; but without effect. The soap-lees being then 
poured out of the tube, and separated from the quicksilver, seemed to be perfectly 
neutralised, and they did not at all discolour paper tinged with the juice of blue 
flowers. Being evaporated to dryness, they left a small quantity of salt, which was 
evidently nitre, as appeared by the manner in which paper, impregnated with a 
solution of it, burned," 

Attempts to repeat Cavendish's experiment in Cavendish's manner have only 
increased the admiration with which we regard this wonderful investigation. 
Working on almost microscopical quantities of material, and by operations extending 
over days and weeks, he thus established one of the most important facts in 
chemistry. And what is still more to the purpose, he raises as distinctly as we 

* " Experiments on Air," < Phil. Trans.,' vol. 75, p. 372, 1785. 

[f The explanation of combustion in Cavendish's day was still vague. It was generally imagined 
that substances capable of burning contained an unknown principle, to which the name i phlogiston ' 
was applied, and which escaped during combustion. Thus, metals and hydrogen and other gases were 
said to be ' phlogisticated ' if they were capable of burning in air. Oxygen being non-inflammable was 
named * dephlogisticated air,' and nitrogen, because it was incapable of supporting combustion or life 
was named by Priestley 'phlogisticated air,' although up till Cavendish's time it had not been made to 
unite with oxygen. 

The term used for oxygen by Cavendish is ' dephlogisticated air,' and for nitrogen, ' phlogisticated 
air/ — April, 1895.] 



could do, and to a certain extent resolves, the question above suggested. - The 
passage is so important that it will be desirable to quote it at full length. 

" As far as the experiments hitherto published extend, we scarcely know more of 
the phlogisticated part of our atmosphere than that it is not diminished by lime- 
water, caustic alkalies, or nitrous air ; that it is unfit to support fire or maintain life 
in animals ; and that its specific gravity is not much less than that of common air ; 
so that, though the nitrous acid, by being united to phlogiston, is converted into air 
possessed of these properties, and consequently, though it was reasonable to suppose, 
that part at least of the phlogisticated air of the atmosphere consists of this acid 
united to phlogiston, yet it was fairly to be doubted whether the whole is of this 
kind, or whether there are not in reality many different substances confounded 
together by us under the name of phlogisticated air. I therefore made an experiment 
to determine whether the whole of a given portion of the phlogisticated air of the 
atmosphere could be reduced to nitrous acid, or whether there was not a part of a 
different nature to the rest which would refuse to undergo that change. The fore- 
going experiments indeed in some measure decided this point, as much the greatest 
part of the air let up into the tube lost its elasticity ; yet as some remained 
unabsorbed it did not appear for certain whether that was of the same nature as the 
rest or not. For this purpose I diminished a similar mixture of dephlogisticated and 
common air, in the same manner as before, till it was reduced to a small part of its 
original bulk. I then, in order to decompound as much as I could of the phlogisti- 
cated air which remained in the tube, added some dephlogisticated air to it and 
continued the spark until no further diminution took place. Having by these means 
condensed as much as I could of the phlogisticated air, I let up some solution of liver 
of sulphur to absorb the dephlogisticated air ; after which only a small bubble of air 
remained unabsorbed, which certainly was not more than y^o °^ ^e bulk of the 
phlogisticated air let up into the tube ; so that, if there is any part of the phlogisti- 
cated air of our atmosphere which differs from the rest, and cannot be reduced to 
nitrous acid, we may safely conclude that it is not more than j^-q part of the whole." 

Although Cavendish was satisfied with his result, and does not decide whether 
the small residue was genuine, our experiments about to be related render it not 
improbable that his residue was really of a different kind from the main bulk of the 
" phlogisticated air," and contained the gas now called argon. 

Cavendish gives data* from which it is possible to determine the rate of absorption 
of the mixed gases in his experiment. The electrical machine used "was one of 
Mr. Naibne's patent machines, the cylinder of which is 12| inches long and 7 in 
diameter. A conductor, 5 feet long and 6 inches in diameter, was adapted to it, and 
the ball which received the spark was placed two or three inches from another ball, 
fixed to the end of the conductor. Now, when the machine worked well, Mr. Gilpin 
supposes he got about two or three hundred sparks a minute, and the diminution of 

* < Phil. Trans./ vol 78, p* 271, 1788. 


the air during* the half hour which he continued working at a time varied in general 
from 40 to 120 measures, but was usually greatest when there was most air in the 
tube, provided the quantity was not so great as to prevent the spark from passing 
readily." The " measure " spoken of represents the volume of one grain of quicksilver, 
or '0048 cub. centim., so that an absorption of one cub. centim. of mixed gas per hour 
was about the most favourable rate. Of the mixed gas about two-fifths would be 

3. Methods of Causing Free Nitrogen to Combine. 

The concord between the determinations of density of nitrogen obtained from 
sources other than the atmosphere, having made it at least probable that some heavier 
gas exists in the atmosphere, hitherto undetected, it became necessary to submit 
atmospheric nitrogen to examination, with a view of isolating, if possible, the unknown 
and overlooked constituent, or it might be constituents. 

Nitrogen, however, is an element which does not easily enter into direct combination 
with other elements ; but with certain elements, and under certain conditions, combi- 
nation may be induced. The elements which have been directly united to nitrogen 
are (a) boron, (b) silicon, (c) titanium, (d) lithium, (e) strontium and barium, 
(/) magnesium, (g) aluminium, (h) mercury, (i) manganese, (J) hydrogen, and 
(k) oxygen, the last two by help of an electrical discharge. 

(a.) Nitride of boron was prepared by Wohler and Deville^ by heating amorphous 
boron to 5 a white heat in a current of nitrogen. Experiments were made to test 
whether the reaction would take place in a tube of difficultly fusible glass ; but it was 
found that the combination took place at a bright red heat to only a small extent, 
and that the boron, which had been prepared by heating powdered boron oxide with 
magnesium dust, was only superficially attacked. Boron is, therefore, not a convenient 
absorbent for nitrogen. [M. Moissan informs us that the reputation it possesses is 
due to the fact that early experiments were made with boron which had been 
obtained by means of sodium, and which probably contained a boride of that metal. 
— April, 1895.] 

(6.) Nitride of silicon^ also requires for its formation a white heat, and complete 
union is difficult to bring about. Moreover, it is not easy to obtain large quantities 
of silicon. This method was therefore not attempted. 

(c.) Nitride of titanium is said to have been formed by Deville and CaroisJ by 
heating titanium to whiteness in a current of nitrogen. This process was not tried 
by us. As titanium has an unusual tendency to unite with nitrogen, it might, 
perhaps, be worth while to set the element free in presence of atmospheric nitrogen, 
with a view to the absorption of the nitrogen. This has, in effect, been already done 

* ' Annales de Chimie, , (3), 52, p. 82. 

t Schutzenberger, ' Oomptes Rendus,' 89, 644. 

J ' Annalen der Chemie u. Pliarmacie,' 101, H60. 

Zx O Zi 


by Wohler and Deville ;* they passed a mixture of the vapour of titanium chloride 
and nitrogen over red-hot aluminium, and obtained a large yield of nitride. It is 
possible that a mixture of the precipitated oxide of titanium with magnesium dust 
might be an effective absorbing agent at a comparatively low temperature. [Since 
writing the above we have been informed by M. Moissan that titanium, heated to 
800°, burns brilliantly in a current of nitrogen. It might therefore be used with 
advantage to remove nitrogen from air, inasmuch as we have found that it does not 
combine with argon.- — April, 1895.] 

(d.), (e.) Lithium at a dull red heat absorbs nitrogen,t but the difficulty of 
obtaining the mefcal in quantity precludes its application. On the other hand, 
strontium and barium, prepared by electrolysing solutions of their chlorides in 
contact with mercury, and subsequently removing the mercury by distillation, are 
said by MaquenneJ to absorb nitrogen with readiness. Although we have not tried 
these metals for removing nitrogen, still our experience with their amalgams has led 
us to doubt their efficacy, for it Is extremely difficult to free them from mercury by 
distillation, and the product is a fused ingot, exposing very little surface to the action 
of the gas. The process might, however, be worth a trial. 

Barium is the efficient absorbent for nitrogen when a mixture of barium carbonate 
and carbon is ignited in a current of nitrogen, yielding cyanide. Experiments have 
shown, however, that the formation of cyanides takes place much more readily and 
abundantly at a high temperature, a temperature not easily reached with laboratory 
appliances. Should the process ever come to be worked on a large scale, the gas 
rejected by the barium will undoubtedly prove a most convenient source of argon. 

(f.) Nitride of magnesium was prepared by Deville and Caron (loo. cit.) during 
the distillation of impure magnesium. It has been more carefully investigated by 
Briegleb and Geuther,§ who obtained it by igniting metallic magnesium in a 
current of nitrogen. It forms an orange-brown, friable substance, very porous, and 
it is easily produced at a bright red heat. When magnesium, preferably in the form 
of thin turnings, is heated in a combustion tube in a current of nitrogen, the tube is 
attacked superficially, a coating of magnesium silicide being formed. As the temperature 
rises to bright redness, the magnesium begins to glow brightly, and combustion takes 
place, beginning at that end of the tube through which the gas is introduced. The 
combustion proceeds regularly, the glow extending down the tube, until all the metal 
has united with nitrogen. The heat developed by the combination is considerable, 
and the glass softens ; but by careful attention and regulation of the rate of the 
current, the tube lasts out an operation. A piece of combustion tubing of the usual 
length for organic analysis packed tightly with magnesium turnings, and containing 

* * Annalen der Chemie u. Pharmacie/ 73, 34. 

f Ouyeard, * Comptes Rendus,' 114, 120. 

X Ouvrard, 4 Comptes Rendus/ 114, 25, and 220. 

4 Annalen der Chemie tl Pharmacie,' 123, 228. 


about 30 grams, absorbs between seven and eight litres of nitrogen. It is essential 
that oxygen be excluded from the tube, otherwise a fusible substance is produced, 
possibly nitrate, which blocks the tube. With the precaution of excluding oxygen, 
the nitride is loose and porous, and can easily be removed from the tube with a rod ; 
but it is not possible to use a tube twice, for the glass is generally softened and 

(g.) Nitride of aluminium has been investigated by Mallet.* He obtained it in 
crystals by heating the metal to whiteness in a carbon crucible. But aluminium 
shows no tendency to unite with nitrogen at a red heat, and cannot be used as an 
absorbent for the gas, 

(li.) GERRESHEiMf states that he has induced combination between nitrogen and 
mercray ; but the affinity between these elements is of the slightest, for the 
compound is explosive. 

(i.) In addition to these, metallic manganese in a finely divided state has been 
shown to absorb nitrogen at a not very elevated temperature, forming a nitride of the 
formula Mn 5 N 3 .J 

(J.) [A mixture of nitrogen, with hydrogen, standing over acid, is absorbed at a 
fair rate under the influence of electric sparks. But with an apparatus such as 
that shown in fig. 1, the efficiency is but a fraction (perhaps £) of that obtainable 
when oxygen is substituted for hydrogen and alkali for acid. — April, 1895.] 

4. Early Experiments on sparking Nitrogen with Oxygen in presence of Alkali. 

In our earliest attempts to isolate the suspected gas by the method of Cavendish, 
we used a Ruhmkoket coil of medium size actuated by a battery of five Grove cells. 
The gases were contained in a test-tube A, fig. 1, standing over a large quantity of 
weak alkali B, and the current was conveyed in wires insulated by U -shaped glass 
tubes CO passing through the liquid round the mouth of the test tube. The inner 
platinum ends DD of the wires were sealed into the glass insulating tubes, but 
reliance was not placed upon these sealings. In order to secure tightness in spite 
of cracks, mercury was placed in the bends. This disposition of the electrodes 
complicates the apparatus somewhat and entails the use of a large depth of liquid in 
order to render possible the withdrawal of the tubes, but it has the great advantage 
of dispensing with sealing electrodes of platinum into the principal vessel, which 
might give way and cause the loss of the experiment at the most inconvenient 
moment. With the given battery and coil a somewhat short spark, or arc, of about 
5 millims. was found to be more favourable than a longer one. When the mixed 
gases were in the right proportion, the rate of absorption was about 30 cub. centims. 

* ' Journ. Ohem. Soc.,' 1876, vol. 2, p. 349. 

f ' Annalen der Ohemie u. Pharmaeie,' 195, 373. 

J O. Pkehlinger, 'Monatsli. f. Cliemie,' 15, 391. 



per hour, or 30 times as fast as Cavendish could work with the electrical machine 
of his day. 

To take an example, one experiment of this kind started with 50 cub. centims, of air. 
To this, oxygen was gradually added until., oxygen being in excess, there was no 
perceptible contraction during an hour's sparking. The remaining gas was then 
transferred at the pneumatic trough to a small measuring vessel, sealed by mercury, 

in which the volume was found to be .1*0 cub. centim. On treatment with alkaline 
pyrogallate, the gas shrank to '32 cub. centim. That this small residue could not be 
nitrogen was argued from the fact that it had withstood the prolonged action of the 
spark, although mixed with oxygen in nearly the most favourable proportion. 

The residue was then transferred to the test-tube with an addition of another 
50 cub. centims. of air, and the whole worked up with oxygen as before. The residue 
was now 2*2 cub. centims., and, after removal of oxygen, # 76 cub. centim. 


Although it seemed almost impossible that these residues could be either nitrogen 
or hydrogen, some anxiety was not unnatural, seeing that the final sparking took 
place under somewhat abnormal conditions. The space was very restricted, and the 
temperature (and with it the proportion of aqueous vapour) was unduly high. But 
any doubts that were felt upon this score were removed by comparison experiments 
in which the whole quantity of air operated on was very small. Thus, when a 
mixture of 5 cub. centims. of air with 7 cub. centims. of oxygen was sparked for one 
hour and a quarter, the residue was *47 cub. centim., and, after removal of oxygen, 
•06 cub. centim. Several repetitions having given similar results, it became clear 
that the final residue did not depend upon anything that might happen when sparks 
passed through a greatly reduced volume, but was in proportion to the amount of air 
operated upon. 

No satisfactory examination of the residue which refused to be oxidised could be 
made without the accumulation of a larger quantity. This, hdwever, was difficult of 
attainment at the time in question. The gas seemed to rebel against the law of 
addition. It was thought that the cause probably lay in the solubility of the gas in 
water, a suspicion since confirmed. At length, however, a sufficiency was collected 
to allow of sparking in a specially constructed tube, when a comparison with the air 
spectrum taken under similar conditions proved that, at any rate, the gas was not 
nitrogen. At first scarcely a trace of the principal nitrogen lines could be seen, but 
after standing over water for an hour or two these lines became apparent. 

[The apparatus shown in fig. 1 has proved to be convenient for the purification of 
small quantities of argon, and for determinations of the amount of argon present in 
various samples of gas, e.g., in the gases expelled from solution in water. To set it 
in action an alternating current is much to be preferred to a battery and break. At 
the Koyal Institution the primary of a small Ktjhmkouff was fed from the 100-volt 
alternating current supply, controlled by two large incandescent lamps in series with 
the coil With this arrangement the voltage at the terminals of the secondary, 
available for starting the sparks, was about 2000, and could be raised to 4000 by 
plugging out one of the lamps. With both lamps in use the rate of absorption of 
mixed gases was 80 cub. centims. per hour, and this was about as much as could well 
be carried out in a test-tube. Even with this amount of power it was found better 
to abandon the sealings at D. No inconvenience arises from the open ends, if the 
tubes are wide enough to ensure the liberation of any gas included over the mercury 
when they are sunk below the liquid. 

The power actually expended upon the coil is very small When the apparatus is 
at work the current taken is only 2*4 amperes. As regards the voltage, by far the 
greater part is consumed in the lamps. The efficient voltage at the terminals of the 
primary coil is best found indirectly. Thus, if A be the current in amperes, V the 
total voltage, V x the voltage at the terminals of the coil, V 3 that at the terminals of 
the lamps, the watts used are 4 '" 

* Ayrton and Sumpner, ' Proc. Roy. Soo.,' vol. 49, p. 427, 1891. 





(V 3 

V 2 3 

In the present case a Oakdew voltmeter gave V 
formula may be neglected. Thus, 

3 ) 

90|, V 2 

= 88 ; and V^ in the 





( V + V 2 ) (V - V 8 ) = A (V - V 8 ) 

2*4 X 2*5 = 6*0 approximately , 

The work consumed by the coil when the sparks are passing is, thus, less than t ^q of 
a horse-power ; but, in designing an apparatus, it must further be remembered that 
in order to maintain the arc, a pretty high voltage is required at the terminals of the 
secondary when no current is passing in it.— April, 1895. 

5. Early Experiments on Withdrawal of Nitrogen from Air by means of Red-hot 


It having been proved that nitrogen, at a bright red heat, was easily absorbed 

by magnesium, best in the form of turnings, an attempt was successfully made to 

remove that gas from the residue left after eliminating oxygen from air by means of 

red-hot copper. 

Fig. 2. 

To SprengeVs 


The preliminary experiment was made in the following manner :— A combustion 
tube, A, was filled with magnesium turnings, packed tightly by pushing them in with 
a rod. This tube was connected with a second piece of combustion tubing, B 5 by 
means of thick-walled india-rubber tubing, carefully wired ; B contained copper oxide, 
and, in its turn, was connected with the tube CD, one-half of which contained soda- 
lime, previously ignited to expel moisture, while the other half was filled with 
phosphoric anhydride. E is a measuring vessel, and F is a gas-holder containing 
" atmospheric nitrogen/' 



In beginning an experiment, the tubes were heated with long-flame burners, and 
pumped empty ; a little hydrogen was formed by the action of the moisture on the 
metallic magnesium ; it was oxidised by the copper oxide and absorbed by the 
phosphoric pentoxide. A gauge attached to the Sprengel's pump, connected with 
the apparatus, showed when a vacuum had been reached. A quantity of nitrogen 
was then measured in E, and admitted into contact with the red-hot magnesium. 
Absorption took place, rapidly at first and then slowly, as shown by the gauge on the 
Sprengei/s pump. A fresh quantity was then measured and admitted, and these 
operations were repeated until no more could be absorbed. The system of tubes was 
then pumped empty by means of the Sprengel's pump, and the gas was collected. 
The magnesium tube was then detached and replaced by another. The unabsorbed 
gas was returned to the measuring-tube by a device shown in the figure (G) and the 
absorption recommenced. After 1094 cub. centims. of gas had been thus treated, 
there was left about 50 cub. centims. of gas, which resisted rapid absorption. It still 
contained nitrogen, however, judging by the diminution of volume which it 
experienced when allowed to stand in contact with red-hot magnesium. Its density 
was, nevertheless, determined by weighing a small bulb of about 40 cub. centims. 
capacity, first with air, and afterwards with the gas. The data are these :— 

(a.) Weight of bulb and air — that of glass counterpoise 

,, alone — that of glass counterpoise . 








(&.) Weight of bulb and gas — that of glass counterpoise 

„ alone — - that of glass counterpoise . 






Taking as the weight of a litre of air, 1*29347 grms., the mean of the latest 
results, and of oxygen (= 16) 1*42961 grms., # the density of the residual gas 

is 14*88. 

* The results on which this and the subsequent calculations are based are as follows (the weights 
are those of 1 litre) : — 

Begnault .... 
Yon Jolly .... 













Regnault's numbers have an approximate correction applied to them by Crafts. The mean of these 



This result was encouraging, although weighted with the unavoidable error attach- 
ing to the weighing of a very small amount. Still the fact remains that the supposed 
nitrogen was heavier than air. It would hardly have been possible to make a mistake 
of 27 milligrams. 

It is right here to place on record the fact that this first experiment was to a great 
extent carried out by Mr. Percy Williams, to whose skill in manipulation and great 
care its success is due, and to whom we desire here to express our thanks. 

Experiments were now begun on a larger scale, the apparatus employed being shown 
in figs. 3 and 4. 

Cu. CiuO. 

(m (h) 




Pi °s 

,. .^vjjE33jj 

A and B are large glass gas-holders of about 10 litres capacity. C is an arrange- 
ment by which gas could be introduced at will into the gas-holder A, either by means 
of an india-rubber tube slipped over the open end of the U-tube, or, as shown in the 
figure, from a test-tube. The tube D was half filled with soda-lime (a), half with 
phosphoric anhydride (b). Similarly, the tube E, which was kept at a red heat by 
means of the long-flame burner, was filled half with very porous copper (a), reduced 
from dusty oxide by heating in hydrogen, half with copper oxide in a granular form (6). 
The next tube, F, contained granular soda-lime, while G contained magnesium turn- 

numbers is taken, that of Regnault for nitrogen being omitted, as there is reason to believe that 
his specimen was contaminated with hydrogen. 



Nitrogen . 





This ratio gives for air the composition by volume 

Oxygen ...*.. 

Nitrogen ...... 

20*91 per cent. 
79-09 „ 

a result verified by experiment. 

It is, of course, to be understood that these densities of nitrogen refer to atmospheric nitrogen, 
that is, to air from which oxygen, water vapour carbon dioxide, and ammonia have been removed. 



ings, also heated to bright redness by means of a long-flame burner. H contained 
phosphoric anhydride, and I soda-lime. All joints were sealed, excepting those 
connecting the hard-glass tubes E and G to the tubes next them. 

The gas-holder A having been filled with nitrogen, prepared by passing air over red- 
hot copper, and introduced at C, the gas was slowly passed through the system of 
tubes into the gas-holder B, and back again. The magnesium in the tube G having 
then ceased to absorb was quickly removed and replaced by a fresh tube. This tube 
was of course full of air, and before the tube G was heated, the air was carried back 
from B towards A by passing a little nitrogen from right to left. The oxygen in the 
air was removed by the metallic copper, and the nitrogen passed into the gas-holder 
A, to be returned in the opposite direction to B. 

Fig. 4 

To Sprengel 's Jg^ 


(a) D (b) 

In the course of about ten days most of the nitrogen had been absorbed. The 
magnesium was not always completely exhausted ; usually the nitride presented the 
appearance of a blackish- yellow mass, easily shaken out of the tube. It is needless to 
say that the tube was always somewhat attacked, becoming black with a coating of 
magnesium silicide. The nitride of magnesium, whether blackish or orange, if left 
for a few hours exposed to moist air, was completely converted into white, dusty 
hydroxide, and during exposure it gave off a strong odour of ammonia. If kept in a 
stoppered bottle, however, it was quite stable. 

It was then necessary, in order to continue the absorption, to carry on operations 
on a smaller scale, with precautions to exclude atmospheric air as completely as 
possible. There was at this stage a residue of 1500 cub. centims. 

The apparatus was therefore altered to that shown in fig. 4, so as to make it possible 
to withdraw all the gas out of the gas-holder A. 

The left-hand exit led to the Sprengei/s pump ; the compartment (a) of the 
drying-tube B was filled with soda-lime, and (&) with phosphoric anhydride. C is a 

2 d 2 


tube into which the gas could be drawn from the gas-holder A. The stop-cock, as 
shown, allows gas to pass through the horizontal tubes, and. does not communicate 
with A ; but a vertical groove allows it to be placed in communication either with the 
gas-holder, or with the apparatus to the right. The compartment (a) of the second 
drying-tube D contained soda-lime, and (b) phosphoric anhydride. The tube D com- 
municated with a hard-glass tube E, heated over a long-flame burner ; it was partly 
filled with metallic copper, and partly with copper oxide; This tube, as well as the 
tube F filled with magnesium turnings, was connected to the drying-tube with india- 
rubber. The gas then entered G, a graduated reservoir, and the arrangement H 
permitted the removal or introduction of gas from or into the apparatus. The gas 
was gradually transferred from the gas-holder to the tube C, and passed backwards 
and forwards over the red-hot magnesium until only about 200 cub. centims. were 
left. It was necessary to change the magnesium tube, which was made of smaller 
size than formerly, several times during the operation* This was done by turning out 
the long-flame burners and pumping off all gas in the horizontal tubes by means of 
the Spren gel's pump. This gas was carefully collected. The magnesium tube was 
then exchanged for a fresh one, and after air had been exhausted from the apparatus, 
nitrogen was introduced from the reservoir. Any gas evolved from the magnesium 
(and apparently there was always a trace of hydrogen, either occluded by the magne- 
sium, or produced by the action of aqueous vapour on the metal) was oxidised by the 
copper oxide. Had oxygen been present, it would have been absorbed by the metallic 
copper, but the copper preserved its red appearance without alteration, whereas a little 
copper oxide was reduced during the series of operations. The gas, which had been 
removed by pumping, was reintroduced at H, and the absorption continued. 

The volume of the gas was thus, as has been said, reduced to about 200 cub. 
centims. It would have been advisable to take exact measurements, but, unfor- 
tunately, some of the original nitrogen had been lost through leakage ; and a natural 
anxiety to see if there was any unknown gas led to pushing on operations as quickly 
as possible. 

The density of the gas was next determined. The bulb or globe in which the gas 
was weighed was sealed to a two-way stop-cock, and the weight of distilled and 
air-free water filling it at 17 # 15° was 162*654 grms., corresponding to a capacity of 
162*843 cub. centims, The shrinkage on removing air completely was 0*0212 cub. 
centim. Its weight, when empty, should therefore be increased by the weight of 
that volume of air, which may be taken as 0*000026 grm. This correction, however, 
is perhaps hardly worth applying in the present case. 

The counterpoise was an exactly similar bulb of equal capacity, and weighing about 
0*2 grm. heavier than the empty globe. The balance was a very sensitive one by 
Oertling, which easily registered one-tenth of a milligrm. By the process of 
swinging, one-hundredth of a milligrm. could be determined with fair accuracy, 

In weighing the empty globe, 0*2 grm, was placed on the same pan as that which 


hung from the end of the beam to which it was suspended, and the final weight was 
adjusted by means of a rider, or by small weights on the other pan. This process 
practically leads to weighing by substitution of gas for weights. The bulb was 
always handled with gloves, to a/void moisture or grease from the fingers. 

Three experiments, of which it is unnecessary to give details, were made to test 
the degree of accuracy with which a gas could be weighed, the gas being dried air, 
freed from carbon dioxide. The mean result gave for the weight of one litre of air 
at 0° and 760 millims, pressure, 1/2935 grm. Regnatjlt found 1*29340, a correction 
having been applied by Crafts to allow for the estimated alteration of volume caused 
by the contraction of his vacuous bulb. The mean result of determinations by several 
observers is 1*29347 ; while one of us found 1*29327. 

The globe was then filled with the carefully' dried gas. 

Temperature, 18 "80°. Pressure, 7 5 9' 3 millims. 

Weight of 162*843 cub. centims. of gas 0*21897 grm. 

"Weight of 1 litre gas at 0° and 760 millims. .... 1*4386 „ 

Density, that of air compared with (), = 16, being 14*476 16100 grms. 

It is evident from these numbers that the dense constituent of the air was being 
concentrated- As a check, the bulb was pumped empty and again weighed ; its 
weight was 0*21903 grm. This makes the density 16*105. 

It appeared advisable to continue to absorb nitrogen from this gas. The first tube 
of magnesium removed a considerable quantity of gas ; the nitride was converted 
into ammonium chloride, and the sample contained 66*30 per cent, of chlorine, 
showing, as has before been remarked, that if any of the heavier constituent of the 
atmosphere had been absorbed, it formed no basic compound with hydrogen. The 
second tube of magnesium was hardly attacked ; most of the magnesium had melted, 
and formed a layer at the lower part of the tube. That which was still left in the 
body of the tube was black on the surface, but had evidently not been much attacked. 
The ammonium chloride which it yielded weighed only 0*0035 grm. 

The density of the remaining gas was then determined. But as its volume was 
only a little over 100 cub. centims., the bulb, the capacity of which was 162 cub. 
centims,, had to be filled at reduced pressure. This was easily done by replacing the 
pear-shaped reservoir of the mercury gas-holder by a straight tube, and noting the 
level of the mercury in the gas-holder and in the tube which served as a mercury 
reservoir against a graduated mirror-scale by help of a cathetomer at the moment of 
closing the stop-cock of the density bulb. 

The details of the experiment are these : — 

Temperature, 19*12° C. Barometric pressure, 749*8 millims. (corr.). 
Difference read on gas-holder and tube, 225*25 millims. (corr.). 
Actual pressure, 524*55 millims. 


Weight of 162*843 cub. centims. of gas . . . . ; 0*17913 grm. 
Weight of 1 litre at 0° and 760 millims. pressure . . 1'7054 ,, 
Density ...... 19*086 grins. 

This gas is accordingly at least 19 times as heavy as hydrogen, 

A portion of the gas was then mixed with oxygen, and submitted to a rapid 
discharge of sparks for four hours in presence of caustic potash. It contracted, and 
on absorbing the excess of oxygen with pyrogallate of potassium the contraction 
amounted to 15*4 per cent, of the original volume. The question then arises, if the 
gas contain 15*4 per cent, of nitrogen , of density 14 e G14, and 84*6 per cent, of other 
gas, and if the density of the mixture were 19 8 086, what would be the density of the 
other gas ? Calculation leads to the number 20 e 0. 

A vacuum-tube was filled with a specimen of the gas of density 19*086, and it 
could not be doubted that it contained nitrogen, the bands of "which were distinctly 
visible. It was probable, therefore, that the true density of the pure gas lay not far 
from 20 times that of hydrogen. At the same time many lines were seen which 
could not be recognized as belonging to the spectrum of any known substance. 

Such were the preliminary experiments made with the aid of magnesium to 
separate from atmospheric nitrogen its dense constituent. The methods adopted in 
preparing large quantities will be subsequently described. 

6. Proof of the Presence of Argon in Air, by means of Atmolysis. 

It has already (§2) been suggested that if " atmospheric ■ nitrogen " contains two 
gases of different densities, it should be possible to obtain direct evidence of the fact 
by the method of atmolysis. The present section contains an account of carefully 
conducted experiments directed to this end. 

The atmolyser was prepared (after Graham) by combining a number of " church- 
warden " tobacco pipes. At first twelve pipes were used in three groups, each group 
including four pipes connected in series. The three groups were then connected in 
parallel, and placed in a large glass tube closed in such a way that a partial vacuum 
could be maintained in the space outside the pipes by a water-pump. One end of 
the combination of pipes was open to the atmosphere, or rather was connected with 
the interior of an open bottle containing sticks of caustic alkali, the object being 
mainly to dry the air. The other end of the combination was connected to a bottle 
aspirator, initially full of water, and so arranged as to draw about two per cent, of 
the air which entered the other end of the pipes. The gas collected was thus a very 
small proportion of that which leaked through the pores of the pipes, and should be 
relatively rich in the heavier constituents of the atmosphere. The flow of water 
from the aspirator could not be maintained very constant, but the rate of two per 
cent, was never much exceeded. The iiecessary four litres took about sixteen hours 
to collect. 



The air thus obtained was treated exactly as ordinary air had been treated in 
determinations of the density of atmospheric nitrogen. Oxygen was removed by 
red-hot copper followed by cupric oxide, ammonia by sulphuric acid, carbonic anhy- 
dride and moisture by potash and phosphoric anhydride. 

The following are the results :— 

Globe empty July 10, 14 . . . 
Globe full September 15 (twelve pipes^ 

Weight of gas ........ 

Ordinary atmospheric nitrogen . . 

Globe empty September 17 ... 
Globe full September 18 (twelve pipes 

"Weight of gas ........ 

Ordinary atmospheric nitrogen . . 

Globe empty September 21 . . . . 
Globe full September 20 (twelve pipes) 

Weight of gas ......... 

Ordinary atmospheric nitrogen . . . 




. + -00487 





. + -00138 





. + -00273 

Globe empty September 21, October 30 
Globe full September 22 (twelve pipes) 

Weight of gas 

Ordinary atmospheric nitrogen . . . 

Difference ....... 

2 9 82306 

. -2-31166 


. + -00150 

The mean excess of the four determinations is -00262 gram., or if we omit the first, 
which depended upon a vacuum weighing of two months old, '00187 gram* 

The gas from prepared air was thus in every case denser than from unprepared air, 
and to an extent much beyond the possible errors of experiment. The excess was, 
however, less than had been expected, and it was thought that the arrangement of 
the pipes could be improved. The final delivery of gas from each of the groups in 
parallel being so small in comparison with the whole streams concerned, it seemed 
possible that each group was not contributing its proper share, and even that there 
might be a flow in the wrong direction at the delivery end of one or two of them. To 


meet this objection, the arrangement in parallel had to be abandoned, and for the 
remaining experiments eight pipes were connected in simple series, The porous 
surface in operation was thus reduced, but this was partly compensated for by an 
improved vacuum. Two experiments were made under the new conditions :— 

Globe empty, October 30, November 5 . . 2*82313 
Globe full, November 3 (eight pipes) . . . '50930 

Weight of gas 2*31383 

Ordinary atmospheric nitrogen . . . . . 2*31016 

Difference ......... + '00367 

Globe empty, November 5, 8 . . . . . . 2*82355 

Globe full, November 6 (eight pipes) . . . . '51011 

Weight of gas .......... 2*31344 

Ordinary atmospheric nitrogen . . . . . 2*31016 

Difference ...... + 9 00328 

The excess being larger than before is doubtless due to the greater efficiency of 
the atmolysing apparatus. It should be mentioned that the above recorded experi- 
ments include all that have been tried, and the conclusion seems inevitable that 
" atmospheric -nitrogen" is a mixture and not a simple body. 

It was hoped that the concentration of the heavier constituent would be sufficient 
to facilitate its preparation in a pure state by the use of prepared air in substitution 
for ordinary air in the oxygen apparatus. The advance of 3 J- mg. on the 11 mg., 
by which atmospheric nitrogen is heavier than chemical nitrogen, is indeed not to be 
despised, and the use of prepared air would be convenient if the diffusion apparatus 
could be set up on a large scale and be made thoroughly self-acting 6 

7. Negative Experiments to Prove that Argon is not derived from Nitrogen or 

from Chemical Sources. 

Although the evidence of the existence of argon in the atmosphere, derived from 
the comparison of densities of atmospheric and chemical nitrogen and from the 
diffusion experiments (§ 6), appeared overwhelming, we have thought it undesirable 
to shrink from any labour that would tend to complete the verification. With this 
object in view, an experiment was undertaken and carried to a conclusion on 
November 13, in which 3 litres of chemical nitrogen, prepared from ammonium 
nitrite, were treated with oxygen in precisely the manner in which atmospheric 
nitrogen had been found to yield a residue of argon. In the course of operations an 


accident occurred, by which no gas could have been lost, but of such a nature that 
from 100 to 200 cub. centims. of air must have entered the working vessel. The gas 
remaining at the close of the large scale operations was w r orked up as usual with 
battery and coil until the spectrum showed only slight traces of the nitrogen lines. 
When cold, the residue measured 4 cub, centims. This was transferred, and after 
treatment with alkaline pyrogallate to remove oxygen, measured 3*3 cub. centims. 
If atmospheric nitrogen had been employed, the final residue should have been about 
30 cub. centims. Of the 3*3 cub. centims. actually left, a part is accounted for by 
the accident alluded to, and the result of the experiment is to show that argon is not 
formed by sparking a mixture of oxygen and chemical nitrogen. 

In a second experiment of the same kind 5660 cub. centims. of nitrogen from 
ammonium nitrite were treated with oxygen in the large apparatus (fig. 7, § 8). The 
final residue was 3*5 cub. centims. ; and as evidenced by the spectrum, it consisted 
mainly of argon. 

The source of the residual argon is to be found in the water used for the 
manipulation of the large quantities of gas (6 litres of nitrogen and 11 litres of 
oxygen) employed. Unfortunately the gases had been collected by allowing them to 
bubble up into aspirators charged with ordinary water, and they were displaced by 
ordinary water. In order to obtain information with respect to the contamination 
that may be acquired in this way, a parallel experiment was tried with carbonic 
anhydride. Eleven litres of the gas, prepared from marble and hydrochloric acid 
with ordinary precautions for the exclusion of air, were collected exactly as oxygen 
was commonly collected. It was then transferred by displacement with water to a 
gas pipette charged with a solution containing 100 grms. of caustic soda. The 
residue which refused absorption measured as much as 110 cub. centims. In another 
experiment where the water employed had been partially de-aerated, the residue left 
amounted to 71 cub. centims., of which 26 cub. centims. were oxygen. The 
quantities of dissolved gases thus extracted from water during the collection of 

J. o o 

oxygen and nitrogen suffice to explain the residual argon of the negative experiments. 
It may perhaps be objected that the impurity was contained in the carbonic 
anhydride itself as it issued from the generating vessel, and was not derived from the 
water in the gas-holder ; and indeed there seems to be a general impression that it is 
difficult to obtain carbonic anhydride in a state of purity. To test this question, 
18 litres of the gas, made in the same generator and from, the same materials, were 
passed directly into the absorption pipette. Under these conditions, the residue was 
only 6|r cub. centims., corresponding to 4 cub. centims. from- 11 litres. The quantity 
of gas employed was determined by decomposing the resulting sodium carbonate with 
hydrochloric acid, allowance being made for a little carbonic anhydride contained in 
the soda as taken from the stock bottle. It will be seen that there is no difficulty 
in reducing the impurity to 3-crdoti 1 , even when india-rubber connections are freely 
used, and no extraordinary precautions are taken. The large amount of impurity 
mdcccxcv. — A. 2 E 


found in the gas when collected over water must therefore have been extracted from 
the water. 

A similar set of experiments was carried out with magnesium. The nitrogen, of 
which three litres were used, was prepared by the action of bleaehing-powder on 
ammonium chloride. It was circulated in the usual apparatus over red-hot magnesium, 
until its volume had been reduced to about 100 cub, centims. An equal volume of 
hydrogen was then added, owing to the impossibility of circulating a vacuum, The 
circulation then proceeded until all absorption had apparently stopped. The remaining 
gas was then passed over red-hot copper oxide into the Spkengei/s pump, and 
collected. As it appeared still to contain hydrogen, which had escaped oxidation, 
owing to its great rarefaction, it was passed over copper oxide for a second and a 
third time, As there was still a residue, measuring 12*5 cub. centims., the gas was 
left in contact with red-hot magnesium for several hours, and then pumped out ; its 
volume was then 4'5 cub. centims. Absorption was, however, still proceeding, when 
the experiment terminated, for at a low pressure, the rate is exceedingly slow, This 
gas, after being sparked with oxygen contracted to 3*0 cub. centims., and on 
examination was seen to consist mainly of argon. The amount of residue obtainable 
from three litres of atmospheric nitrogen should have amounted to a large multiple 
of this quantity. 

In another experiment, 15 litres of nitrogen prepared from, a mixture of ammonium 
chloride and sodium nitrite by warming in a flask (some nitrogen having first been 
drawn off by a vacuum-pump, in order to expel all air from the flask and from the 
contained liquid) were collected over water in a large gas-holder. The nitrogen was 
not bubbled through the water, but was admitted from above, while the water escaped 
below. This nitrogen was absorbed by red-hot magnesium, contained in tubes heated 
in a combustion-furnace. The unabsorbed gas was circulated over red-hot magnesium 
in a special small apparatus, by which its volume was reduced to 15 cub. centims. 
As it was impracticable further to reduce the volume by means of magnesium, the 
residual 15 cub. centims. were transferred to a tube, mixed with oxygen, and submitted 
to sparking over caustic soda. The residue after absorption of oxygen, which 
undoubtedly consisted of pure argon, amounted to 3*5 cub. centims. This is one-fortieth 
of the quantity which would have been obtained from atmospheric nitrogen, and its 
presence can be accounted for, we venture to think, first from the water in the 
gas-holder, which had not been freed from dissolved gas by boiling in vacuo (it has 
already been shown that a considerable gain may ensue from this source), and second, 
from leakage of air which accidentally took place, owing to the breaking of a tube. 
The leakage may have amounted to 200 cub. centims., but it could not be accurately 
ascertained. Quantitative negative experiments of this nature are exceedingly 
difficult, and require a long time to carry them to a successful conclusion. 


8. Separation of Argon on a Large Scale. 

To separate nitrogen from " atmospheric nitrogen " on a large scale, by help of 
magnesium, several devices were tried. It is not necessary to describe them all in 
detail. Suffice it to say that an attempt was made to cause a store of " atmospheric 
nitrogen " to circulate by means of a fan, driven by a water -motor. The difficulty 
encountered here was leakage at the bearing of the fan, and the introduced air 
produced a cake which blocked the tube on coming into contact with the magnesium. 
It might have been possible to remove oxygen by metallic copper ; but instead of 
thus complicating the apparatus, a water-injector was made use of to induce circula- 
tion. Here also it is unnecessary to enter into details. For, though the plan worked 
well, and although about 120 litres of "atmospheric nitrogen" were absorbed, the 
yield of argon was not large, about 600 cub. eentims. having been collected. This 
loss was subsequently discovered to be due partially, at least, to the relatively high 
solubility of argon in water. In order to propel the gas over magnesium, through a 
long combustion-tube packed with turnings, a considerable water-pressure, involving 
a large flow of water, was necessary. The gas was brought into intimate contact 
with this water, and presuming that several thousand litres of water ran through the 
injector, it is obvious that a not inconsiderable amount of argon must have been 
dissolved. Its proportion was increasing at each circulation, and consequently its 
partial pressure also increased. Hence, towards the end of the operation, at least, 
there is every reason to believe that a serious loss had occurred. 

It was next attempted to pass " atmospheric nitrogen " from a gas-holder first 
through a combustion tube of the usual length packed with metallic copper reduced 
from the oxide ; then through a small U-tube containing a little water 5 which was 
intended as an index of the rate of flow ; the gas was then dried by passage through 
tubes filled with soda-lime and phosphoric anhydride ; and it next passed through a 
long iron tube (gas-pipe) packed with magnesium turnings, and heated to bright 
redness in a second combustion-furnace. 

After the iron tube followed a second small U -tube containing water, intended to 
indicate the rate at which the argon escaped into a small gas-holder placed to receive 
it. The nitrogen was absorbed rapidly, and argon entered the small gas-holder. But 
there was reason to suspect that the iron tube is permeable by argon at a red heat. 
The first tube-full allowed very little argon to pass. After it had been removed and 
replaced by a second, the same thing was noticed. The first tube was difficult to 
clean ; the nitride of magnesium forms a cake on the interior of the tube, and it was 
very difficult to remove it ; moreover this rendered the filling of the tube very 
troublesome, inasmuch as its interior was so rough that the magnesium turnings could 
only with difficulty be forced down. However, the permeability to argon, if such be 
the case, appeared to have decreased. The iron tube was coated internally with a 
skin of magnesium nitride, which appeared to diminish its permeability to argon. 

Al E )u 



After all the magnesium in the tube had been converted into nitride (and this was 
easily known, because a bright glow proceeded gradually from one end of the tube to 
the other) the argon remaining in the iron tube was ( ' washed " out by a current of 
nitrogen ; so that after a number of operations, the small gas-holder contained a 
mixture of argon with a considerable quantity of nitrogen. 

On the whole, the use of iron tubes is not to be recommended, owing to the diffi- 
culty in cleaning them, and the possible loss through their permeability to argon. 
There is no such risk of loss with glass tubes, but each operation requires a new tube, 
and the cost of the glass is considerable if much nitrogen is to be absorbed. Tubes 
of porcelain were tried ; but the glaze in the interior is destroyed by the action of the 
red-hot magnesium, and the tubes crack on cooling. 

By these processes 157 litres of "atmospheric nitrogen" were reduced in volume to 
about 2 9 5 litres in all of a mixture of nitrogen and argon. This mixture was after- 
wards circulated over red-hot magnesium, in order to remove the last portion of 

Fig*. 5. 

To Bpre/igel's 

As the apparatus employed for this purpose proved very convenient, a full descrip- 
tion of its construction is here given. A diagram is shown in fig. 5, which sufficiently 
explains the arrangement of the apparatus. A is the circulator. It consists of a sort 
of Sprengel's pump (a) to which a supply of mercury is admitted from a small 


reservoir (b). This mercury is delivered into a gas-separator (c), and the mercury 
overflows into the reservoir (d). When its level rises, so that it blocks the tube {f)> 
it ascends in pellets or pistons into (e), a reservoir which is connected through (g) 
with a water-pump. The mercury falls into (6), and again passes down the Spkengel 
tube (a). No attention is, therefore, required, for the apparatus works quite auto- 
matically. This form of apparatus was employed several years ago by Dr. Collie. 

The gas is drawn from the gas-holder B, and passes through a tube 0, which is 
heated to redness by a long-flame burner, and which contains in one half metallic 
copper, and in the other half copper oxide. This precaution is taken in order to remove 
any oxygen which may possibly be present, and also any hydrogen or hydrocarbon. 
In practice, it was never found that the copper became oxidised, or the oxide reduced. 
It is, however, useful to guard against any possible contamination. The gas next 
traversed a drying-tube D, the anterior portion containing ignited soda-lime, and the 
posterior portion phosphoric anhydride. From this it passed a reservoir, D', from 
which it could be transferred, when all absorption had ceased, into the small gas- 
holder. It then passed through E, a piece of combustion-tube, drawn out at both 
ends, filled with magnesium turnings, and heated by a long-flame burner to redness. 
Passing through a small bulb, provided with electrodes, it again entered the fall 

After the magnesium tube E had done its work, the stop-cocks were all closed, and 
the gas was turned down, so that the burners might cool. The mixture of argon and 
nitrogen remaining in the system of tubes was pumped out by a Sprengel's pump 
through F, collected in a large test-tube, and reintroduced into the gas-holder B 
through the side-tube G, which requires no description. The magnesium tube was 
then replaced by a fresh one ; the system of tubes was exhausted of air ; argon and 
nitrogen were admitted from the gas-holder B ; the copper-oxide tube and the 
magnesium tube were again heated ; and the operation was repeated until absorption 
ceased. It was easy to decide when this point had been reached, by making use of 
the graduated cylinder H, from which water entered the gas-holder B. It was found 
advisable to keep all the water employed in these operations, for it had become 
saturated with argon. If gas was withdrawn from the gas-holder, its place was taken 
by this saturated water. 

The absorption of nitrogen proceeds very slowly towards the end of the operation, 
and the diminution in volume of the gas is not greater than 4 or 5 cub. centims. per 
hour. It is, therefore, somewhat difficult to judge of the end-point, as will be seen 
when experiments on the density of this gas are described. The magnesium tube, 
towards the end of the operations, was made so hot that the metal was melted in the 
lower part of the tube, and sublimed in the upper part. The argon and residual 
nitrogen had, therefore, been thoroughly mixed with gaseous magnesium during its 
passage through the tube E. 

To avoid possible contamination with air in the Sprengel's pump, the last portion 


of gas collected from, the system of tubes was not re-admitted to the gas-holder B, but 
was separately stored. 

The crude argon was collected In two operations. First, the quantity made by 
absorption by magnesium in glass tubes with the water-pump circulator was purified. 
Later, after a second supply had been prepared by absorption In iron tubes, the mixture 
of argon and nitrogen was united with the first quantity and circulated by means of the 
mercury circulator, in the gas-holder B. Attention will be drawn to the particular 
sample of gas employed in describing further experiments made with the argon. 

By means of magnesium, about 7 litres of nitrogen can be absorbed in an hour. 
The changing of the tubes of magnesium, however, takes some time ; consequently, 
the largest amount absorbed in one day was nearly 30 litres. 

At a later date a quantitative experiment was carried out on a large scale, the 
amount of argon from 100 litres of "atmospheric" nitrogen, measured at 20°, having 
been absorbed by magnesium, and the resulting argon measured at 12°. During the 
process of absorbing nitrogen in the combustion-furnace, however, one tube cracked, 
and it is estimated that about 4 litres of nitrogen escaped before the crack was 
noticed. With this deduction, and assuming that the nitrogen had been measured at 
12°, 93*4 litres of atmospheric nitrogen were taken. The magnesium required for 
absorption weighed 409 grms. The amount required by theory should have been 
285 grms. ; but it must be remembered that in many cases the magnesium was by no 
means wholly converted into nitride. The first operation yielded about 3 litres of a 
mixture of nitrogen and argon, which was purified in the circulating apparatus. The 
total residue, after absolution of the nitrogen, amounted to 921 cub. centims. The 
yield is therefore 0*986 per cent. 

At first no doubt the nitrogen gains a little argon from the water over which it 
stands. But, later, when the argon forms the greater portion of the gaseous mixture, 
its solubility in water must materially decrease its volume. It is difficult to estimate 
the loss from this cause. The gas-holder, from which the final circulation took place 
held three litres of water. Taking the solubility of argon as 4 per cent., this would 
mean a loss of about 120 cub. centims. If this is not an over-estimate, the yield of 
argon would be increased to 1040 cub. centims., or 1*11 per cent. The truth probably 
lies between these two estimates. 

It may be concluded, with probability, that the argon forms approximately 1 per 
cent, of the " atmospheric " nitrogen. 

The principal objection to the oxygen method of isolating argon, as hitherto 
described, is the extreme slowness of the operation, An absorption of 30 cub. 
centims. of mixed gas means the removal of but 12 cub. centims, of nitrogen. At 
this rate 8 hours are required for the isolation of 1 cub. centim. of argon, supposed 
to be present in the proportion of 1 per cent. 

In extending the scale of operations we had the great advantage of the advice of 


Mr. Crookes, who a short time ago called attention to the flame rising from platinum 
terminals, which convey a high tension alternating electric discharge, and pointed 
out its dependence . upon combustion of the nitrogen and oxygen of the air.* 
Mr. was kind enough to arrange an impromptu demonstration at his own 
house with a small alternating current plant, in which it appeared that the absorp- 
tion of mixed gas was at the rate of 500 cub. centims. per hour, or nearly 20 times 
as fast as with the battery. The arrangement is similar to that first described by 
SpoTTiswooDE.t The primary of a Ruhmkoree coil is connected directly with the 
alternator, no break or condenser being required. ; so that, in fact, the coil acts 
simply as a high potential transformer. When the arc is established the platinum 
terminals may be separated much beyond the initial striking distance, s 

The plant with which the large scale operations have been made consists of a 
De Meritens alternator, kindly lent by Professor J. J. Thomson, and a gas engine. 
As transformer, one of Swinburne's hedgehog pattern has been employed with 
success, but the ratio of transformation (24 : 1) is scarcely sufficient. A higher 
potential, although, perhaps, not more efficient, is more convenient. The striking 
distance is greater, and the arc is not so liable to go out. Accordingly most of the 
work to be described has been performed with transformers of the Ruhmkoree type. 

The apparatus has been varied greatly, and it cannot be regarded as having even 
yet assumed a final form. But it will give a sufficient idea of the method if we 
describe an experiment in which a tolerably good account was kept of the air and 
oxygen employed. The working vessel was a glass flask, A (fig. 6), of about 1500 cub. 
centims. capacity, and stood, neck downwards, over a large jar of alkali, B. As in 
the small scale experiments, the leading-in wires were insulated by glass tubes, DD, 
suitably bent and carried through the liquid up the neck. "For the greater part of 
the length iron wires were employed, but the internal extremities, EE, were of 
platinum, doubled upon itself at the terminals from which the discharge escaped. 
The glass protecting tubes must be carried up for some distance above the internal 
level of the liquid, but it is desirable that the arc itself should not be much raised 
above that level. A general idea of the disposition of the electrodes will be obtained 
from fig. 6. To ensure gas tightness the bends were occupied by mercury. A tube, 
C, for the supply or withdrawal of gas was carried in the same way through the 

The Ruhmkoree employed in this operation was one of medium size. When the 
mixture was rightly proportioned and the arc of full length, the rate of absorption 
was about 700 cub. centims. per hour. A good deal of time is lost in starting, for, 
especially when there is soda on the platinums, the arc is liable to go out if lengthened 
prematurely. After seven days the total quantity of air let in amounted to 7925 cub. 
centimse, and of oxygen (prepared from chlorate of potash) 9137 cub. centims. On 

* ' Chemical News,' vol. 65, p. 301, 1892. 

t " A Mode of Exciting an Induction-coil," * Phil. Mag.,' vol. 8, p. 890, 1879. 



the eighth and ninth days oxygen alone was added, of which about 500 cub. centims. 
was consumed, while there remained about 700 cub. centims in the flask. Hence the 
proportion in which the air and oxygen combined was as 70 : 96. On the eighth day 
there was about three hours' work, and the absorption slackened off to about one 
quarter of the previous rate. On the ninth day (September 8) the rate fell off still 

Fig. 6, 

more, and after three hours' work became very slow. The progress towards removal 
of nitrogen was examined from time to time wLth the spectroscope, the points being 
approximated and connected with a small Leyden jar. At this stage the yellow 
nitrogen line was faint, but plainly visible. After about four hours' more work, the 
yellow line had disappeared, and for two hours there had been no visible contraction. 
It will be seen that the removal of the last part of the nitrogen was very slow, mainly 
on account of the large excess of oxygen present. 


The final treatment of the residual 700 cub. centitns. of gas was on the model of 
the small scale operations already described (§ 4). By means of a pipette the gas was 
gradually transferred to a large test-tube standing over alkali. Under the influence 
of sparks (from battery and coil) passing all the while, the superfluous oxygen was 
consumed with hydrogen fed in slowly from a voltameter. If the nitrogen had been 
completely removed, and if there were no unknown ingredient in the atmosphere, the 
volume under this treatment should have diminished without limit. But the con- 
traction stopped at a volume of 65 cub. centims., and the volume was taken back- 
wards and forwards through this as a minimum by alternate treatment with oxygen 
and hydrogen added in small quantities, with prolonged intervals of sparking. 
Whether the oxygen or the hydrogen were in excess could be determined at any 
moment by a glance at the spectrum. At the minimum volume the gas was certainly 
not hydrogen or oxygen. Was it nitrogen ? On this point the testimony of the 
spectroscope was equally decisive. No trace of the yellow nitrogen line could be seen 
even with a wide slit and under the most favourable conditions. 

When the gas stood for some days, over water the nitrogen line again asserted 
itself, and many hours of sparking with a little oxygen were required again to get rid of 
it. As it was important to know what proportions of nitrogen could be made visible 
in this way, a little air was added to gas that had been sparked for some time subse- 
quently to the disappearance of nitrogen in its spectrum. It was found that about 
1| per cent, was clearly, and about 3 per cent, was conspicuously, visible. About the 
same numbers apply to the visibility of nitrogen in oxygen when sparked under these 
conditions, that is, at atmospheric pressure, and with a jar in connection with the 
secondary terminals. 

When we attempt to increase the rate of absorption by the use of a more powerful 
electric arc, further experimental difficulties present themselves. In the arrangement 
already described, giving an absorption of 700 cub. centims. per hour, the upper part 
of the flask becomes very hot. With a more powerful arc the heat rises to such a 
point that the flask is filled with steam and the operation comes to a standstill. 

It is necessary to keep the vessel cool by either the external or internal application 
of liquid to the upper surface upon which the hot gases from the arc impinge. One 
way of effecting this is to cause a small fountain of' alkali to impinge on the top of 
the flask, so as to wash the whole of the upper surface. This plan is very effective, 
but it is open to the objection that a break-down would be disastrous, and it would 
involve special arrangements to avoid losing the argon by solution in the large 
quantity of alkali required. It is simpler in many respects to keep the vessel cool by 
immersing it in a large body of water, and the inverted flask arrangement (fig. 6) has 
been applied in this manner. But, on the whole, it appears to be preferable to limit 
the application of the cooling water to the upper part of the external surface, building 
up for this purpose a suitable wall of sheet lead cemented round the glass. The most 




convenient apparatus for large-scale operations that has hitherto been tried is shown 
in the accompanying figure (fig. 7). 

The vessel A is a large globe of about 6 litres capacity, intended for demonstrating 
the combustion of phosphorus in oxygen gas, and stands in an inclined position. It 
is about half filled with a solution of caustic soda. The neck is fitted with a rubber 
stopper, B, provided with four perforations. Two of these are fitted with tubes, 
C, D 9 suitable for the supply or withdrawal of gas or liquid. The other two allow 
the passage of the stout glass tubes, E, F, which contain the electrodes. For greater 
security against leakage, the interior of these tubes is charged with water, held in 
place by small corks, and the outer ends are cemented up. The electrodes are formed 

Fig. 7. 


of stout iron wires terminated by thick platinums, G, H, triply folded together, and 
welded at the ends. The lead walls required to enclose the cooling water are 
partially shown at I. For greater security the india-rubber cork is also drowned in 
water, held in place with the aid of sheet-lead. The lower part of the globe is 
occupied by about 3 litres of a 5 per cent, solution of caustic soda, the solution rising 
to within about half-an-inch of the platinum terminals. With this apparatus an 
absorption of 3 litres of mixed gas per hour can be attained, —about 3000 times the 
rate at which Cavendish could work. 

When it is desired to stop operations, the feed of air (or of chemical nitrogen in 
blank experiments) is cut off, oxygen alone being supplied as long as any visible 
absorption occurs. Thus at the close the gas space is occupied by argon and oxygen 
with such nitrogen as cannot readily be taken up in a condition of so great dilution. 


The oxygen, being too much for convenient treatment with hydrogen, was usually 
absorbed with copper and ammonia, and the residual gas was then worked over again 
as already described in an apparatus constructed upon a smaller scale. 

It is worthy of notice that with the removal of the nitrogen, the arc-discharge from 
the dynamo changes greatly in appearance, bridging over more directly and in a nar- 
rower band from one platinum to the other, and assuming a beautiful sky-blue colour, 
instead of the greenish hue apparent so long as oxidation of nitrogen is in progress. 

In all the large-scale experiments, an attempt was made to keep a reckoning of the 
air and oxygen employed, in the hope of obtaining data as to the proportional 
volume of argon in air, but various accidents too often interfered. In one successful 
experiment (January, 1895), specially undertaken for the sake of measurement, the 
total air employed was 9250 cub. centims., and the oxygen consumed, manipulated 
with the aid of partially de-aerated water, amounted to 10,820 cub. centims. The 
oxygen contained in the air would be 1942 cub. centims. ; so that the quantities of 
"atmospheric nitrogen" and of total oxygen which enter into combination would be 
7308 cub. centims., and 12,762 cub. centims. respectively. This corresponds to 
N + 1*750 — the oxygen being decidedly in excess of the proportion required to form 
nitrous acid — 2HN0 2 , or H 3 + N 3 +30. The argon ultimately found on absorption 
of the excess of oxygen was 75'0 cub. centims., reduced to conditions similar to 
those under which the air was measured, or a little more than 1 per cent, of the 
" atmospheric nitrogen" used. It is probable, however, that some of the argon was 
lost by solution during the protracted operations required in order to get quit of the 
last traces of nitrogen. 

[In recent operations at the Eoyal Institution, where a public supply of alternating 
current at 100 volts is available, the scale of the apparatus has been still further 

The capacity of the working vessel is 20 litres, of which about one half is 
occupied by a strong solution of caustic soda. The platinum terminals are very 
massive, and the flame rising from them is prevented from impinging directly upon 
the glass by a plate of platinum held over it and supported by a wire which passes 
through the rubber cork. In the electrical arrangements we have had the advantage 
of Mr. Swinburne's advice. The transformers are two of the « hedgehog 1 ' pattern, 
the thick wires being connected in parallel and the thin wires in series. In order to 
control the current taken when the arc is short or the platinums actually in contact, 
a choking-coil, provided with a movable core of fine iron wires, is inserted in the 
thick wire circuit. In normal working the current taken from the mains is about 
22 amperes, so that some 2| h. p. is consumed. At the same time the actual 
voltage at the platinum terminals is 1500. When the discharge ceases, the voltage 
at the platinum rises to 3000, # which is the force actually available for re-starting 
the discharge if momentarily stopped. 

* A still higher voltage on open circuit would be preferable. 

2 F 2 


With this discharge, the rate of absorption of mixed gases is about 7 litres per hour. 
When the argon has accumulated to a considerable extent, the rate falls off, and after 
several days' work, about 6 litres per hour becomes the maximum. In commencing 
operations it is advisable to introduce, first, the oxygen necessary to combine with 
the already included air, after which the feed of mixed gases should consist of about 
1 1 parts of oxygen to 9 parts of air. The mixed gases may be contained in a large 
gas-holder, and then, the feed being automatic, very little attention is required. 
When it is desired to determine the rate of absorption, auxiliary gas-holders of glass, 
graduated into litres, are called into play. If the rate is unsatisfactory, a determina- 
tion may be made of the proportion of oxygen in the working vessel, and the 
necessary gas, air, or oxygen, as the case may be, introduced directly. 

In re-starting the arc after a period of intermission, it is desirable to cut off the 
connection with the principal gas-holder. The gas (about two litres in amount) 
ejected from the working vessel by the expansion is then retained in the auxiliary 
holder, and no argon finds its way further baok. The connection between the working 
vessel and the auxiliary holder should be made without india-rubber, which is liable 
to be attacked by the ozonized gases. 

The apparatus has been kept in operation for fourteen hours continuously, and 
there should be no difficulty in working day and night. An electric signal could 
easily be arranged to give notice of the extinction of the arc, which sometimes occurs 
unexpectedly ; or an automatic device for re-striking the arc could be contrived.— 
April, 1895.] 

9. Density of Argon prepared by means of Oxygen. 

A first estimate of the density of argon prepared by the oxygen method was 
founded upon the data recorded already respecting the volume present in air, on the 
assumption that the accurately known densities of " atmospheric " and of chemical 
nitrogen differ on account of the presence of argon in the former, and that during the 
treatment with oxygen nothing is oxidised except nitrogen. Thus, if 

D = density of chemical nitrogen, 

D' = ,, atmospheric nitrogen, 

d = „ argon, 

a = proportional volume of argon in atmospheric nitrogen, 

the law of mixtures gives 

ad + (l— a)D = D 


d = D + (D' - D)/a. 


In this formula D' — ■ D and a are both small, but they are known with fair 
accuracy. From the data already given for the experiment of September 8th 

„ _- _ — ____£. •_ 0*01 04 * 

0-79 x 7925 J 

whence, if on an arbitrary scale of reckoning D = 2*2990, D' = 2*3102, we find 
d = 3*378. Thus if N 2 be 14, or 3 be 16, the density of argon is 20*6. 
Again, from the January experiment, 

a =-i£ = °- 0103 ' 

whence, if N = 14, the density of argon is 20*6, as before. There can be little doubt, 

however, that these numbers are too high, the true value of a being greater than is 

supposed in the above calculations. 

A direct determination by weighing is desirable, but hitherto it has not been 

feasible to collect by this means sufficient to fill the large globe (§1) employed for 

other gases. A mixture of about 400 cub. centims. of argon with pure oxygen, 

however, gave the weight 2*7315, 0*1045 in excess of the weight of oxygen, viz., 

2*6270. Thus, if a be the ratio of the volume of argon to the whole volume, the 

number for argon will be 

2*6270 + 0-1045/a. 

The value of a, being involved only in the excess of weight above that of oxygen, 
does not require to be known very accurately. Sufficiently concordant analyses by two 
methods gave a = 0*1845 ; whence, for the weight of the gas we get 3*193 ; so that 
if O = 16, the density of the gas would be 19*45. An allowance for residual nitrogen, 
still visible in the gas before admixture of oxygen, raises this number to 19*7, which 
may be taken as the density of pure argon resulting from this determination.* 

10. Density of Argon Prepared by means of Magnesium.f 

It has already been stated that the density of the residual gas from the first and 
preliminary attempt to separate oxygen and nitrogen from air by means of mag- 
nesium was 19*086, and allowing for contraction on sparking with oxygen the density 
is calculable as 20*01. The following determinations of density were also made : — 

(a.) After absorption in glass tubes, the water circulator having been used, and 
subsequent circulation by means of mercury circulator until rate of contraction had 

* [The proportion of nitrogen (4 or 5 per cent, of the volume) was estimated from the appearance of 
the nitrogen lines in the spectrum, these being somewhat more easily visible than when 3 per cent, 
of nitrogen was introduced into pure argon (§ 8), — April, 1895.] 

f See Addendum, p. 237. 


become slow, 162*843 cub. centims., measured at 757*7 millims. (corr.) pressure, and 
16*81° C, weighed 0*2683 grm. Hence, 

Weight of 1 litre at 0° and 760 millims. , . , 17543 grms. 
Density compared with hydrogen (0 = 16) . . 19*63 ,, 

This gas was again circulated over red-hot magnesium for two days. Before 
circulation It contained nitrogen as was evident from its spectrum ; after circulating, 
nitrogen appeared to be absent, and absorption had completely stopped. The density 
was again determined. 

(6.) 162,843 cub. centims., measured at 745*4 millims. (corr.) pressure, and 
17*25° C, weighed 0*2735 grm. Hence, 

Weight of 1 litre at 0° and 760 millims. . . . 1*8206 grms. 
Density compared with hydrogen (O = 16) . . 20*38 ,, 

Several portions of this gas, having been withdrawn for various purposes, were 
somewhat contaminated with air, owing to leakage, passage through the pump, &c. 
All these portions were united in the gas-holder with the main stock, and circulated 
for eight hours, during the last three of which no contraction occurred. The gas 
removed from the system of tubes by the mercury-pump was not restored to the 
gas-holder, but kept separate. 

(c.) 162*843 cub. centims., measured at 758*1 millims. (corr.) pressure, and 
17*09° C, weighed 0*27705 grm. Hence, 

Weight of 1 litre at 0° and 760 millims, . . . 1*8124 grms. 
Density compared with hydrogen (O = 16) . . 20*28 ,, 

The contents of the gas-holder were subsequently increased by a mixture of 
nitrogen and argon from 37 litres of atmospheric nitrogen, and after circulating, 
density was determined. The absorption was however not complete. 

(d.) 162*843 cub. centims,, measured at 767*6 millims. (corr.) pressure, and 
16*31° C, weighed 0*2703 grm. Hence, 

Weight of 1 litre at 0° and 760 millims. . . 1*742 grms. 

Density compared with hydrogen (O = 16) . . . 19*49 ,, 

The gas was further circulated, until all absorption had ceased. This took about 
six hours. Density was again determined. 

(e.) 1 62*843 cub. centims. measured at 767*7 millims. (corr.) pressure, and 15*00° C, 
weighed 0*2773 grm. Hence, 

Weight of 1 litre at 0° and 760 millims. . , . 1*7784 grms. 
Deinsity compared with hydrogen (O = 16) . . 19*90 ,, 


(f.) A second determination was carried out, without further circulation. 
162*843 cub. centims. measured at 769*0 millims. (corr.) pressure, and 16*00° C, 
weighed 0*2757 grm. Hence, 

Weight of 1 litre at 0° and 760 millims. . , , 1*7713 grais. 
Density compared with hydrogen (O = 16) , * . 19*82 „ 

(g.) After various experiments had been made with the same sample of gas, it was 
again circulated until all absorption ceased. A vacuum-tube was filled with it, and 
showed no trace of nitrogen. 

The density was again determined : — 

162*843 cub. centims. measured at 750 millims. (corr.) pressure, and at 15*62° C, 
weighed 0*26915 grm. 

Weight of 1 litre at 0° and 760 millims. , . . 1*7707 grms. 
Density compared with hydrogen (O = 16). . . 19*82 ,, 

These comprise all the determinations of density made. It should be stated that 
there was some uncertainty discovered later about the weight of the vacuous globe in 
(b) and (c). Rejecting these weighings, the mean of (e), (f), and (g) is 19*88, The 
density may be taken as 19*9, with approximate accuracy. 

It is better to leave these results without comment at this point, and to return 
to them later. 

11. Spectrum of Argon. 

Vacuum tubes were filled with argon prepared by means of magnesium at various 
stages in this work, and an examination of these tubes has been undertaken by 
Mr. Crookes, to whom we wish to express our cordial thanks for his kindness in 
affording us helpful information with regard to its spectrum. The first tube was 
filled with the early preparation of density 19*09, which obviously contained some 
nitrogen. A photograph of the spectrum was taken, and compared with a photograph 
of the spectrum of nitrogen, and it was at once evident that a spectrum different from 
that of nitrogen had been registered. 

Since that time many other samples have been examined. 

The spectrum of argon, seen in a vacuum tube of about 3 millims. pressure, consists 
of a great number of lines, distributed over almost the whole visible field. Two lines 
are specially characteristic ; they are less refrangible than the red lines of hydrogen or 
lithium, and serve well to identify the gas when examined in this way. Mr. Crookes, 
who gives a full account of the spectrum in a separate communication, has kindly 
furnished us with the accurate wave-lengths of these lines as well as of some others 
next to be described; they are respectively 696*56 and 705*64 X 10~ 6 millim. 

Besides these red lines, a bright yellow line, more refrangible than the sodium line, 


occurs at 603*84. A group of five bright green lines occurs next, besides a number of 
less intensity* Of this group of five, the second, which is perhaps the most brilliant, 
has the wave-length 561*00. There is next a blue, or blue-violet, line of wave-length 
470*2 and last, in the less easily visible pa,rt of the spectrum, there are five strong 
violet lines, of which the fourth, which is the most brilliant, has the wave- 
length 420*0, 

Unfortunately, the red lines, which are not to be mistaken for those of any other 
substance, are only to be seen at atmospheric pressure when a very powerful jar- 
discharge is passed through argon. The spectrum, seen under these conditions, has 
been examined by Professor Schuster. The most characteristic lines are perhaps 
those in the neighbourhood of F, and are very easily seen if there be not too much 
nitrogen, in spite of the presence of some oxygen and water- vapour. The approximate 
wave-lengths are :— 

487*91 . . . . . Strong. 

(486*07) ...... F. 

484*71 . . . . . Not quite so strong. 

480*52 . . . . . Strong 


473*53 y . . . . Fairly strong* characteristic triplet, 

4 / Z*Dt> J 

It is necessary to anticipate Mr. Crookes's communication, and to state that when 
the current is passed from the induction-coil in one direction, that end of the capillary 
tube next the positive pole appears of a redder, and that next the negative of a bluer 
hue. There are, in effect, two spectra, which Mr, Crookes has succeeded in separat- 
ing to a considerable extent. Mr. E. C. C. Baly, # who has noticed a similar phe- 
nomenon, attributes it to the presence of two gases. The conclusion would follow that 
what we have termed " argon " is in reality a mixture of two gases which have as yet 
not been separated. This conclusion, if true, is of great importance, and experiments 
are now in progress to test it by the use of other physical methods. . The full bearing 
of this possibility will appear later. 

A comparison was made of the spectrum seen in a vacuum tube with the spectrum 
in a "plenum" tube, i.e. y one filled at atmospheric pressure. Both spectra were 
thrown into a field at the same time. It was evident that they were identical, 
although the relative strengths of the lines were not always the same. The seventeen 
most striking lines were absolutely coincident. 

The presence of a small quantity of nitrogen interferes greatly with the argon 
spectrum. But we have found that in a tube with platinum electrodes, after the 

* ' Proc. Phys. Soc.,' 1893, p. 147. He says : " When an electric current is passed through a mixture 
of two gases, one is separated from the other, and appears in the negative glow." 


discharge has been passed for four hours, the spectrum of nitrogen disappears, and 
the argon spectrum manifests itself in full purity. A specially constructed tube, with 
magnesium electrodes, which we hoped would yield good results, removed all traces 
of nitrogen it is true, but hydrogen was evolved from the magnesium, and showed its 
characteristic lines very strongly. However, these are easily identified. The gas 
evolved on heating magnesium in vacuo, as proved by a separate experiment, consists 
entirely of hydrogen. 

Mr. Grookes has proved the identity of the chief lines of the spectrum of gas 
separated from air-nitrogen by aid of magnesium with that remaining after sparking 
air- nitrogen with oxygen, in presence of caustic soda solution. 

Professor Schuster has also found the principal lines identical in the spectra of 
the two gases, when taken from the jar discharge at atmospheric pressure. 

12, Solubility of Argon in Water. 

The tendency of the gas to disappear when manipulated over water in small 
quantities having suggested that it might be more than usually soluble in that liquid, 
special experiments were tried to determine the degree of solubility. 

The most satisfactory measures relating to the gas isolated by means of oxygen 
were those of September 28. The sample contained a trace of oxygen, and (as 
judged by the spectrum) a residue of about 2 per cent, of nitrogen. The procedure 
and the calculations followed pretty closely the course marked out by Bunsen, # and 
it is scarcely necessary to record the details. The quantity of gas operated upon was 
about 4 cub. centims., of which about 1|> cub. centims. were absorbed. The final 
result for the solubility was 3*94 per 100 of water at 12° C, about 2^ times that of 
nitrogen. Similar results have been obtained with argon prepared by means of 
magnesium. At a temperature of 13*9°, 131 arbitrary measures of water absorbed 
5*3 of argon. This corresponds to a solubility in distilled water, previously freed 
from dissolved gas by boiling in vacuo for a quarter of an hour, and admitted to the 
tube containing argon without contact with air, of 4*05 cub. centims. of argon per 
100 of water. 

The fact that the gas is more soluble than nitrogen would lead us to expect it in 
increased proportion in the dissolved gases of rain water. Experiment has confirmed 
this anticipation. Some difficulty was at first experienced in collecting a sufficiency 
for the weighings in the large globe of nearly 2 litres capacity. Attempts at 
extraction by means of a Topler pump without heat were not very successful. It was 
necessary to operate upon large quantities of water, and then the pressure of the 
liquid itself acted as an obstacle to the liberation of gas from all except the upper 
layers, Tapping the vessel with a stick of wood promotes the liberation of gas in a 

* ' Grasometry/ p. 141. 



remarkable manner, but to make this method effective, some means of circulating the 
water would have to be introduced. 

The extraction of the gases by heat proved to be more manageable. Although a 
large quantity of water has to be brought to or near 100° C, a prolonged boiling is 
not necessary, as it is not a question of collecting the whole of the gas contained in 
the water. The apparatus employed, which worked very well after a little experience, 
will be understood from the accompanying figure. The boiler A was constructed 

Fig. 8. 


from an old oil-can, and was heated by an ordinary ring Bunsen burner. For the 
supply and removal of water, two co-axial tubes of thin brass, and more than four feet 
in length, were applied upon the regenerative principle. The outgoing water flowed 
in the inner tube BC, continued from C to D by a prolongation of composition 
tubing. The inflowing water from a rain-water cistern was delivered into a glass 
tube at E, and passed through a brass connecting tube FG into the narrow annular 
space between the two principal tubes GEL The neck of the can was fitted with an 
india-rubber cork and delivery-tube, by means of which the gases were collected in 


the ordinary way. Any carbonic anhydride was removed by alkali before passage 
into the glass aspirating bottles used as gas-holders. 

The convenient working of this apparatus depends very much upon the mainten- 
ance of a suitable relation between the heat and the supply of water. It is desirable 
that the water in the can should actually boil, but without a great development of 
steam ; otherwise not only is there a waste of heat, and thus a smaller yield of gas, 
but the inverted flask used for the collection of the gas becomes inconveniently hot and 
charged with steam. It was found desirable to guard against this by the application 
of a slow stream of water to the external surface of the flask. When the supply of 
water is once adjusted, nearly half a litre of gas per hour can be collected with very 
little attention. 

The gas, of which about four litres are required for each operation, was treated 
with red-hot copper, cupric oxide, sulphuric acid, potash, and finally phosphoric anhy- 
dride, exactly as atmospheric nitrogen was treated in former weighings. The weights 
found, corresponding to those recorded in § 1, were on two occasions, 2*3221 and 
2*3227, showing an excess of 24 milligrms. above the weight of true nitrogen. Since 
the corresponding excess for atmospheric nitrogen is 11 milligrms., we conclude 
that the water-nitrogen is relatively twice as rich in argon. 

Unless some still better process can be found, it may be desirable to collect the 
gases ejected from boilers, or from large supply pipes which run over an elevation, 
with a view to the preparation of argon upon a large scale. 

The above experiments relate to rain water. As regards spring water, it is known 
that many thermal springs emit considerable quantities of gas, hitherto regarded as 
nitrogen. The question early occurred to us as to what proportion, if any, of the 
new gas was contained therein. A. notable example of a nitrogen spring is that at 
Bath, examined by Daubeny in 1833. With the permission of the authorities of 
Bath, Dr. Arthuk Bichardson was kind enough to collect for us about 10 litres of 
the gases discharged from the King's Spring. A rough analysis on reception showed, 
that it contained scarcely any oxygen and but little carbonic anhydride. Two 
determinations of density were made, the gas being treated in all respects as air, 
prepared by diffusion and unprepared, were treated for the isolation of atmospheric 

nitrogen. The results were :— 


October 29 ........... . 2*30513 

November 7 ........... . 2*30532 

ivxean « » , » . . « . . » » Zl'o\ju£Jj 

The weight of the "nitrogen" from the Bath gas is thus about halfway between 
that of chemical and " atmospheric ?? nitrogen, suggesting that the proportion of 
argon is less than in air, instead of greater as had been expected. 

& Ct a 



13. Behaviour at Loiv Temperatures. 

A single experiment was made with an early sample of gas,, of density 19*1, 
which certainly contained a considerable amount of nitrogen. On compressing it in a 
pressure apparatus to between 80 and 100 atmospheres pressure, and cooling to 
— 90° by means of boiling nitrous oxide, no appearance of liquefaction could be 
observed. As the critical pressure was not likely to be so high as the pressure to 
which it had been exposed, the non-liquefaction was ascribed to insufficient cooling. 

This supposition turned out to be correct. For, on sending a sample to Professor 
Olszewski, the author of most of the accurate measurements of the constants of 
gases at low temperatures, he was kind enough to submit it to examination. His 
results are published elsewhere; but, for convenience of reference, his tables, showing 
vapour-pressures, and giving a comparison between the constants of argon and those 
of other gases, are here reproduced. 





Pressure. Temperature. 


35-8 atms. 
38-0 „ 
50*6 „ 

- 186-9 

- 138-3 

740 '5 millims. 
23'7 atms. 

- 136^2 

- 135-] 

- 134-4 

! o 
27*3 atms. j - 129*4 

29-0 „ - 128-6 

29-8 „ - 121-0 


Hydrogen, H 

Nitrogen, Ng . . . . 
Carbon monoxide, CO 
Argon, A l . . . . . 

Oxygen, 3 . . . . 
Nitric oxide, ISTO . . 
Methane, CH 4 . . . 






- 93-5 

— ol'o 



















of liquid 


of gas. 

at boiling- 





























Colour of 





14. The ratio of the Bpeeifie Heats of Argon* 

In order to decide regarding the elementary or compound nature of argon, 
experiments were made on the velocity of sound in it. It will, be remembered that 
from the velocity of sound, the ratio of the specific heat at constant pressure to that 
at constant volume can be deduced by means of the equation 

# See Addendum, p. 239, 


£> jL <J 




1 + a 

; C, J 

where n is the frequency, X is the wave-length of sound, v its velocity, e the 
isothermal elasticity, d the density, (1 + at) the temperature-correction, C ;J the 
specific heat at constant pressure, and G v that at constant volume. In comparing 
two gases at the same temperature, each of which obeys Boyle's law with sufficient 
approximation and in using the same sound, many of these factors disappear, and the 
ratio of specific heats of one gas may be deduced from that of the other, if known, 
by the simple proportion 

Xhl :X'*d' : : 1*408 


where for example X and d refer to air, of which the ratio is 1*408, according to 
the mean of observations by Rontgen (1*4053), Wullner (1*4053), Kayser (1*4106), 
and Jamin and Richard (1*41). 

The apparatus employed, although in principle the same as that usually employed, 
differed somewhat from the ordinary pattern, inasmuch as the tube was a narrow one, 
of 2 millims. bore, and the vibrator consisted of a glass rod, sealed into one end of 
the tube, so that about 15 centims. projected outside the tube, while 15 centims. was 
contained in the tube. By rubbing the projecting part longitudinally with a rag wet 
with alcohol, vibrations of exceedingly high pitch of the gas contained in the tube 
took place, causing waves which registered their nodes by the usual device of 
lycopodium powder. The temperature was that of the atmosphere and varied little 
from 17*5°; the pressure was also atmospheric, and varied only one millim. during 
the experiments. Much of the success of these experiments depends on so adjusting 
the length of the tube as to secure a good echo, else the wave-heaps are indistinct. 
But this is easily secured by attaching to its open end a piece of thick-walled india- 
rubber tubing, which can be closed by a clip at a spot which is found experimentally 
to produce good heaps at the nodes. 

The accuracy of this instrument has frequently been tested ; but fresh experiments 
were made with air, carbon dioxide, and hydrogen, so as to make certain that 
reasonably reliable results were obtainable. Of these an account is here given. 

Gras in tube. 


oi observations. 

Half- wave-length. 

Ratio — £ • 






• • 
• » 

-Air .... 
OOg .... 
J7JL3 . , . , 



• • 



1*408 Assumed 
1-276 Found 
1-376 Found 

To compare these results with those of previous observers, the following numbers 



were obtained for carbon dioxide :—Cazin, l e 29L; Bontgen, 1*305; De Lucchi, 
1*292; Mulleii, 1*265; Wullner, 1*311; Dulong, 1*339; Masson, 1'274; Keg- 
nau'LT, 1*268; Amagat, 1*299 ; and Jamin and Richard, 1*29, It appears just to 
reject Dulong's number, which deviates so markedly from the rest ; the mean of 
those remaining is 1*288, which is in sufficient agreement with that given above. 
For the ratio of the specific heats of hydrogen, we have :— Cazin, 1*410 ; Rontgeist, 
1*385 ; Dulong, 1*407 ; Masson, 1*401 ; Kegnatjlt, 1*400 ; and Jamin and Richard, 
1*4.10. The mean of these numbers is 1*402. This number appears to differ con- 
siderably from the one given above. But it must be noted, first, that the wave- 
length which should have been found is 74*5, a number differing but little from that 
actually found ; second, that the waves were long and that the nodes were somewhat 
difficult to place exactly ; and third, that the atomic weight of hydrogen has been 
taken as unity, whereas it is more likely to be 1*01, if oxygen, as was done, be taken 
as 16, The atomic weight 1*01 raises the found value of the ratio to 1*399, a number 
differing but little from the mean value found by other observers. 

Having thus established the trustworthiness of the method, we proceed to describe 
our experiments with argon. 

Five series of measurements were made with the sample of gas of density 19*82. 
It will be remembered that a previous determination with the same gas gave as its 
density 19*90. The mean of these two numbers was therefore taken as correct, 
viz., 19*86. 

The individual measurements are :— - 














for the half- wave-length. Calculating the ratio of the specific heats, the number 
1*644 is obtained. 

The narrowness of the tube employed in these experiments might perhaps raise a 
doubt regarding the accuracy of the measurements, for it is conceivable that in 
so narrow a tube the viscosity of the gas might affect the results. We therefore 
repeated the experiments, using a tube of 8 millims. internal diameter. 

The mean of eleven readings with air, at 18°, gave a half-wave-length of 
34*62 millims. With argon in the same tube, and at the same temperature, the 
half- wave-length was, as a mean of six concordant readings, 31*64 millims. The 
density of this sample of argon, which had been transferred from a water gas-holder 
to a mercury gas-holder, was 19*82 ; and there is some reason to suspect the presence 
of a trace of air, for it had been standing for some time. 

The result, however, substantially proves that the ratio previously found was 


correct. In the wide tube, C^ : C v : : 1*61 : 1. Hence the conclusion must be 
accepted that the ratio of specific heats is practically 1*66 : 1. 

It will be noticed that this is the theoretical ratio for a monatomic gas, that is, a 
gas in which all energy imparted to it at constant volume is expended in effecting 
translational motion. The only other gas of which the ratio of specific heats has 
been found to fulfil this condition is mercury at a high temperature. # The extreme 
importance of these observations will be discussed later. 

15. Attempts to induce Chemical Combination. 

A great number of attempts were made to induce chemical combination with 
the argon obtained by use of magnesium, but without any positive result. In such a 
case as this, however, it is necessary to chronicle negative results, if for no other 
reason but that of justifying its name, " argon." These will be detailed in order. 

(a) Oxygen in Presence of Caustic Alkali. — This need not be further discussed 
here ; the method of preparing argon is based on its inactivity under such con- 

(6) Hydrogen. — It has been mentioned that, in order to free argon from excess of 
oxygen, hydrogen was admitted, and sparks passed to cause combination of hydrogen 
and oxygen. Here again caustic alkali was present, and argon appeared to be 

A separate experiment was, however, made in absence of water, though no special 
pains was taken to dry the mixture of gases. The argon was admitted up to half an 
atmosphere pressure into a bulb, through whose sides passed platinum wires, carrying 
pointed poles of gas-carbon. Hydrogen was then admitted until atmospheric pressure 
had been attained. Sparks were then passed for four hours by means of a large 
induction coil, actuated by four storage cells. The gas was confined in a bulb closed 
by two stop-cocks, and a small V-tube with bulbs was interposed, to act as a gauge, 
so that if expansion or contraction had taken place, the escape or entry of gas would 
be observable. The apparatus, after the passage of sparks, was allowed to cool to 
the temperature of the atmosphere, and, on opening the stop-cock, the level of water 
in the V-tube remained unaltered. It may therefore be concluded that, in all 
probability, no combination has occurred ; or, that if it has, it was attended w r ith no 
change of volume. 

(c) Chlorine. — Exactly similar experiments were performed with dry, and after- 
wards with moist, chlorine. The chlorine had been stored over strong sulphuric acid 
for the first experiment, and came in contact with dry argon. Three hours sparking 
produced no change of volume. A drop of water was admitted into the bulb. After 
four hours sparking, the volume of the gas, after cooling, was diminished by about 

* Kundt and Warburg, ' Pogg. Aim,,' 157, p. 353, 1876. 


Yg- cub. centim., due probably to the solution of a little chlorine in the small quantity 
of water present. 

(d) Phosphorus.-— A piece of combustion-tubing, closed at one end, containing at 
the closed end a small piece of phosphorus, was sealed to the mercury reservoir 
containing argon ; connected to the same reservoir was a mercury gauge and a 
Sprengei/s pump. After removing all air from the tubes, argon was admitted to a 
pressure of 600 millims. The middle portion of the combustion-tube was then heated 
to bright redness, and the phosphorus was distilled slowly from back to front, so that 
its vapour should come into contact with argon at a red heat. When the gas was hot, 
the level of the gauge altered ; but, on cooling, it returned to its original level, 
showing that no contraction had taken place. The experiment was repeated several 
times, the phosphorus being distilled through the red-hot tube from open to closed 
end, and vice versa. In each case, on cooling, no change of pressure was remarked. 
Hence it may be concluded that phosphorus at a red-heat is without action on argon. 
It may be remarked parenthetically that no gaseous compound of phosphorus is 
known, which does not possess a volume different from the sum of those of its 
constituents. That no solid compound was formed is sufficiently proved by the 
absence of contraction. The phosphorus was largely converted into the red modifica- 
tion during the experiment. 

(e) Sulphur —An exactly similar experiment was performed with sulphur, again 
with negative results. It may therefore be concluded that sulphur and argon are 
without action on each other at a red heat. And again, no gaseous compound of 
sulphur is known in which the volume of the compound is equal to the sum of those 
of its constituents. 

(/) Tellurium.— As this element has a great tendency to unite with heavy metals, 
it was thought worth while to try its action. In this, and in the experiments to be 
described, a different form was given to the apparatus. The gas was circulated over 
the reagent employed, a tube containing it being placed in the circuit. The gas was 
dried by passage over soda-lime and phosphoric anhydride ; it then passed over the 
tellurium or other reagent, then through drying tubes, and then back to the gas- 
holder. That combination did not occur was shown by the unchanged volume of gas 
in the gas-holder ; and it was possible, by means of the graduated cylinder which 
admitted water to the gas-holder, to judge of as small an absorption as half a cubic 
centimeter. The tellurium distilled readily in the gas, giving fche usual yellow 
vapours ; and it condensed, quite unchanged, as a black sublimate. The volume of 
the gas, when all was cold, was unaltered. 

(g) Sodium.— A piece of sodium, weighing about half a gramme, was heated in argon. 
It attacked the glass of the combustion tube, which it blackened, owing to liberation 
of silicon ; but it distilled over in drops into the cold part of the tube. Again no 
change of volume occurred, nor was the surface of the distilled sodium tarnished ; it 
was brilliant, as it is when sodium is distilled in vacuo. It may probably also be 


concluded from this experiment that silicon, even while being liberated, is without 
action on argon. 

The action of compounds was then tried ; those chosen were such as lead to oxides 
or sulphides. Inasmuch as the platinum-metals, which are among the most inert of 
elements, are attacked by fused caustic soda, its action was investigated. 

(A) Fused and Red-hot Caustic Soda. — The soda was prepared from sodium, in an 
iron boat, by adding drops of water cautiously to a lump of the metal. When action 
had ceased, the soda was melted, and the boat introduced into a piece of combustion- 
tube placed in the circuit. After three hours circulation no contraction had occurred. 
Hence caustic soda has no action on argon. 

(i) Soda-lime at a red-heat.— Thinking that the want of porosity of fused caustic 
soda might have hindered absorption, a precisely similar experiment was carried out 
with soda-lime, a mixture which can be heated to bright redness without fusion. 
Again no result took place after three hours heating. 

(j) Fused Potassium Nitrate was tried under the impression that oxygen plus a 
base might act where oxygen alone failed. The nitrate w r as fused, and kept at a 
bright red heat for two hours, but again without any diminution in volume of the 

(k) Sodium Peroxide. — Yet another attempt was made to induce combination with 
oxygen and a base, by heating sodium peroxide to redness in a current of argon for 
over an hour, bat also without effect. It is to be noticed that metals of the platinum 
group would have entered into combination under such treatment. 

(I) Persidphides of Sodium and Calcium. — Soda-lime was heated to redness in 
an open crucible, and some sulphur was added to the red-hot mass, the lid of the 
crucible being then put on. Combination ensued, with formation of polysulphides 
of sodium and calcium. This product was heated to redness for three hours in a 
brisk current of argon, again with negative result. Again, metals of the platinum 
group would have combined under such treatment. 

(m) Some argon was shaken in a tube with nitix)- hydrochloric acid. On addition 
of potash, so as to neutralise the acid, and to absorb the free chlorine and nitrosyl 
chloride, the volume of the gas was barely altered. The slight alteration was evidently 
due to solubility in the aqueous liquid, and it may be concluded that no chemical 
action took place. 

(n) Bromine-water was also without effect. The bromine vapour was removed 
with potash. 

(o) A mixture of potassium permanganate and hydrochloric acid, involving the 
presence of nascent chlorine, had no action, for on absorbing chlorine by means of 
potash, no alteration in volume had occurred. 

( p) Argon is not absorbed by platinum black. A current was passed over a pure 
specimen of this substance ; as usual, however, it contained occluded oxygen. There 
was no absorption in the cold. At 100°, no action took place; and on heating to 



redness, by which the black was changed to sponge, still no evidence of absorption 
was noticed. In all these experiments, absorption of half a cubic centimetre of argon 
could have at once been detected. 

We do not claim to have exhausted the possible reagents. But this much is 
certain, that the gas deserves the name " argon," for it is a most astonishingly indif- 
ferent body, inasmuch as it is unattacked by elements of very opposite character, 
ranging from sodium and magnesium on the one hand, to oxygen, chlorine, and 
sulphur on the other. It will be interesting to see if fluorine also is without action, 
but for the present that experiment must be postponed, on account of difficulties of 

It will also be necessary to try whether the inability of argon to combine at 
ordinary or at high temperatures is due to the instability of its possible compounds, 
except when cold. Mercury vapour at 800° would present a similar instance of 
passive behaviour. 

16. General Conclusions. 

It remains, finally, to discuss the probable nature of the gas or gases which we 
have succeeded in separating from atmospheric air, and which has been provisionally 
named argon. 

That argon is present in the atmosphere, and is not manufactured during the 
process of separation is amply proved by many lines of evidence. First, atmospheric 
nitrogen has a high density, while chemical nitrogen is lighter. That chemical 
nitrogen is a uniform substance is proved by the identity of properties of samples 
prepared by several different processes, and from several different compounds. It 
follows, therefore, that the cause of the high density of atmospheric nitrogen is due 
to the admixture with heavier gas. If that gas possesses the density of 20 compared 
with hydrogen as unity, atmospheric nitrogen should contain of it approximately 
1 per cent. This is found to be the case, for on causing the nitrogen of the atmos- 
phere to combine with oxygen in presence of alkali, the residue amounted to about 
1 per cent. ; and on removing nitrogen with magnesium the result is similar. 

Second : This gas has been concentrated in the atmosphere by diffusion. It is true 
that it cannot be freed from oxygen and nitrogen by diffusion, but the process of 
diffusion increases relatively to nitrogen the amount of argon in that portion which 
does not pass through the porous walls. That this is the case is proved by the 
increase of density of that mixture of argon and nitrogen. 

Third : On removing nitrogen from " atmospheric nitrogen " by means of magne- 
sium, the density of the residue increases proportionately to the concentration of the 
heavier constituent. 

Fourth : As the solubility of argon in water is relatively high, it is to be expected 
that the density of the mixture of argon and nitrogen, pumped out of water 
along with oxygen should, after removal of the oxygen, exceed that of " atmos- 
pheric nitrogen." Experiment has shown that the density is considerably increased. 


Fifth : It is in the highest degree improbable that two processes, so different from 
each other, should each manufacture the same product. The explanation is simple if 
it be granted that these processes merely eliminate nitrogen from " atmospheric 

Sixth : If the newly discovered gas were not in the atmosphere, the discrepancies 
in the density of " chemical " and " atmospheric " nitrogen would remain unexplained. 

Seventh : It has been shown that pure nitrogen, prepared from its compounds, 
leaves a negligible residue when caused to enter into combination with oxygen or 
with magnesium. 

There are other lines of argument which suggest themselves ; but we think that it 
will be acknowledged that those given above are sufficient to establish the existence 
of argon in the atmosphere. 

It is practically certain that the argon prepared by means of electric sparking with 
oxygen is identical with argon prepared by means of magnesium. The samples have 
in common :— 

First : Spectra which have been found by Mr. Orookes, Professor Schuster, and 
ourselves to be practically identical. 

Second : They have approximately the same density. The density of argon, pre- 
pared by means of magnesium, was 19*9 ; that of argon, from sparking with oxygen, 
about 19*7 ; these numbers are practically identical. 

Third : Their solubility in water is the same. 

That argon is an element, or a mixture of elements, may be inferred from the 
observations of § 1 4. For Clausius has shown that if K be the energy of translatory 
motion of the molecules of a gas, and H their whole kinetic energy, then 

*L _ 3 (gg - a ) 

Jtl 2i\jy 

C p and C v denoting as usual the specific heat at constant pressure and at constant 
volume respectively. Hence, if, as for mercury vapour and for argon (§ 14), the 
ratio of specific heats C p : C. v be If, it follows that E^ = H, or that the whole kinetic 
energy of the gas is accounted for by the translatory motion of its molecules. In the 
case of mercury the absence of interatomic energy is regarded as proof of the mon- 
atomic character of the vapour, and the conclusion holds equally good for argon. 

The only alternative is to suppose that if argon molecules are di- or polyatomic, 
the atoms acquire no relative motion, even of rotation, a conclusion improbable in 
itself and one postulating the sphericity of such complex groups of atoms. 

Now a monatomic gas can be only an element, or a mixture of elements ; and 
hence it follows that argon is not of a compound nature. 

According to Avogadbo, equal volumes of gases at the same temperature and 
pressure, contain equal numbers of molecules. The molecule of hydrogen gas, the 
density of which is taken as unity, is supposed to consist of two atoms. Its mole- 

2 TT O 


cular weight is therefore 2. Argon is approximately 20 times as heavy as hydrogen, 
that is, its molecular weight is 20 times as great as that of hydrogen, or 40. But its 
molecule is mon atomic, hence its atomic weight, or, if it be a mixture, the mean of 
the atomic weights of the elements in that mixture, taken for the proportion in which 
they are present, must be 40. 

This conclusion rests on the assumption that all the molecules of argon are mon- 
atomic. The result of the first experiment is, however, so nearly that required by 
theory, that there is room for only a small number of molecules of a different 
character. A study of the expansion of argon hj heat is proposed, and would 
doubtless throw light upon this question. 

There is evidence both for and against the hypothesis that argon is a mixture : for, 
owing to Mr. Crook es's observations of the dual character of its spectrum ; against, 
because of Professor Olszewski's statement that it has a definite melting-point, a 
definite boiling-point, and a definite critical temperature and pressure ; and because 
on compressing the gas in presence of its liquid, pressure remains sensibly constant 
until all gas has condensed to liquid. The latter experiments are the well-known 
criteria of a pure substance ; the former is not known with certainty to be character- 
istic of a mixture. The conclusions which follow are, however, so startling, that in 
our future experimental work we shall endeavour to debide the question by other 

For the present, however, the balance of evidence seems to point to simplicity. 
We have, therefore, to discuss the relations to other elements of an element of atomic 
weight 40. We inclined for long to the view that argon was possibly one, or more 
than one, of the elements which might be expected to follow fluorine in the periodic 
classification of the elements— elements which should have an atomic weight between 
19, that of fluorine, and 23, that of sodium. But this view is apparently put out of 
court by the discovery of the monatomic nature of its molecules. 

The series of elements possessing atomic weights near 40 are : — 

Chlorine 35 6 5 

Potassium 39'1 

Calcium 40 '0 

Scandium 44*0. 

There can be no doubt that potassium, calcium, and scandium follow legitimately 
their predecessors in the vertical columns, lithium, beryllium, and boron, and that 
they are in almost certain relation with rubidium, strontium, and (but not so 
certainly) yttrium. If argon be a single element, then there is reason to doubt 
whether the periodic classification of the elements is complete ; whether, in fact, 
elements may not exist which cannot be fitted among those of which it is composed. 
On the other hand, if argon be a mixture of two elements, they might find place in 
the eighth group, one after chlorine and one after bromine. Assuming 37 (the 


approximate mean between the atomic weights of chlorine and potassium) to be the 
atomic weight of the lighter element, and 40 the mean atomic weight found, and 
supposing that the second element has an atomic weight between those of bromine, 
80, and rubidium, 85*5, viz., 82, the mixture should consist of 93*3 per cent, of the 
lighter, and 6*7 per cent, of the heavier element. But it appears improbable that 
such a high percentage as 6'7 of a heavier element should have escaped detection 
during liquefaction. 

If the atomic weight of the lighter element were 38, instead of 37, however, the 
proportion of heavier element would be considerably reduced. Still, it is difficult to 
account for its not having been detected, if present. 

If it be supposed that argon belongs to the eighth group, then its properties would 
fit fairly well with what might be anticipated. For the series, which contains 

O • IV p III and V QIl to VI QTir l pi I to VII 

>OL n , ■ 14 , Pgto2 j ctllU Vyl 2 •> 

might be expected to end with an element of monatomic molecules, of no valency, i.e., 
incapable of forming a compound, or if forming one, being an octad ; and it would 
form a possible transition to potassium, with its monovalence, on the other hand, 
Such conceptions are, however, of a speculative nature ; yet they may be perhaps 
excused, if they in any way lead to experiments which tend to throw more light on 
the anomalies of this curious element. 

In conclusion, it need excite no astonishment that argon is so indifferent to reagents. 
For mercury, although a monatomic element, forms compounds which are by no means 
stable at a high temperature in the gaseous state ; and attempts to produce compounds 
of argon may be likened to attempts to cause combination between mercury gas at 
800° and other elements. As for the physical condition of argon, that of a gas, we 
possess no knowledge why carbon, with its low atomic weight, should be a solid, while 
nitrogen is a gas, except in so far as we ascribe molecular complexity to the former 
and comparative molecular simplicity to the latter. Argon, with its comparatively 
low density and its molecular simplicity, might well be expected to rank among the 
gases. And its inertness, which has suggested its name, sufficiently explains why it 
has not previously been discovered as a constituent of compound bodies. 

We would suggest for this element, assuming provisionally that it is not a mixture, 
the symbol A. 

We have to record our thanks to Messrs. Gordon, Kellas, and Matthews, and 
especially to Mr. Percy Williams, for their assistance in the prosecution of this 

Addendum (by Professor W. Eamsay). 

March 20, 1895. 

Further determinations of the density of argon prepared by means of magnesium 
have been made. In each case the argon was circulated over magnesium for at least 



two hours after "all absorption of nitrogen had stopped, as well as over red-hot 

copper, copper oxide, soda-lime, and phosphoric anhydride. The gas also passed out 

of the mercury gas-holder through phosphoric anhydride into the weighing globe. 

The results are in complete accordance with previous determinations of density ; and 

for convenience of reference the former numbers are included in the table which 


Density of Argon. 





mil lira s. 



Weight of 
1 litre at 

0° and 760 

(0 = 16). 

(1) Nov. 26 . . . 
\"j ,, ii( . » . 

(3) Dec. 22 . . . 

(4) Feb. 16 . . . 

(5) „ 19 . . . 

(6) „ 24 . . . 

cub. centims. 













i i 

The general mean is 19*900 ; or if Nos. (2) and (3) be rejected as suspiciously low, 
the mean of the remaining four determinations is 19'94L The molecular weight may 
therefore be taken as 39*9 without appreciable error. 

The value of R in the gas-equation R = pv/T has also been determined between 
— 89° and + 248°. For this purpose, a gas- thermometer was filled with argon, and 
a direct comparison was made with a similar thermometer filled with hydrogen. 

The method of using such a hydrogen -thermometer has already been described by 
Ramsay and Shields.* For the lowest temperature, the thermometer bulbs were 
immersed in boiling nitrous oxide; for atmospheric temperature, in running water; 
for temperatures near 100° in steam, and for the remaining temperatures, in the 
vapours of chlorobenzene, aniline, and quinolene. 

The results are collected in the following tables :— 

Hydrogen Thermometer, 



Volume (corr.). 






1 -00036 









2*6701 I 









- 87-92 




* * Trans. Chem. Soc./ vol. 63, pp. 835, 836. It is to be noticed that the value of R is not involved 
in using the hydrogen-thermometer; its constancy alone is postulated. 


/■iO J 

The value of R is thus practically constant, and this affords a proof that the four 
last temperatures have been estimated with considerable accuracy. 

Argon Thermometer. 




Volume (eorr.). 



Seines L . . 

























By mischance, air leaked into the bulb ; it was therefore refilled. 

feeries 11. 






1200 3 



A bubble of argon leaked into the bulb, and the value of R increased. 

beries 111. . 





















It may be concluded from these numbers, that argon undergoes no molecular 
change between -—88° and + 250°. 

Further determinations of the wave-length of sound in argon have been made, the 
wider tube having been used. In every case the argon was as carefully purified as 
possible. In experiment (3) too much lycopodium dust was present in the tube ; 
that is perhaps the cause of the low result. For completeness' sake, the original 
result in the narrow tube has also been given. 



19 97 

Half -wave-length, 



In air. 

In arg'on. 



Jd eD. -LO ..•».. 



Ox ul 


17 ? 5 







The general mean of these numbers is 1*643; if (3) be rejected, it is 1*648. In 
the last experiment every precaution was taken. The half-wave-length in air is 
the mean of 11 readings, the highest of which was 34*67 and the lowest 34*00. 
They run :— 


34'67 ; 34*06 ; 34'27 ; 34*39; 34*00; 34*00; 34-13; 34*20; 34*20; 34*33; 34*33. 
11*25°; 11*00°; 10*80"; 10 8° ; 10*0°; 11*0° ; 11-3° ; 11'4° ; 11-4° ; 11*6° ; 11*6° 

With, argon the mean is also that of 11 readings, -of which the highest is 31*83, 
and the lowest, 31*5. They are :— 

31*5 ; 31*5 ; 31*66 ; 31*55 ; 31*83 ; 31*77 ; 31*81 ; 31*83; 31'83; 31-50; 31-66. 
11*8°; 11*8°; 11*20°; 11*40°; 11*60°; 11-40°; 11*40°; 11*4° ; 11*5° ; 11*5°; 11*4°. 

If the atomic weight of argon is identical with its molecular weight, it must closely 
approximate to 39*9. But if there were some molecules of A 2 present, mixed with a 
much larger number of molecules of A x , then the atomic weight would be corres- 
pondingly reduced. Taking an imaginary case, the question may be put :— -What 
percentage of molecules of A 3 would raise the density of A l from 19*0 to 19*9 ? A 
density of 19*0 would imply an atomic weight of 38*0, and argon would fall into the 
gap between chlorine and potassium. Calculation shows that in 10,000 molecules, 
474 molecules of A 3 would have this result, the remaining 9526 molecules being 
those of A P 

Now if molecules of A a be present, it is reasonable to suppose that their number 
would be increased by lowering the temperature, and diminished by heating the gas, 
A larger change; of density should ensue on lowering than, on raising the temperature, 
however, as onthe above supposition, there is not a large proportion of molecules of 
A 2 present. 

But it must be acknowledged that the constancy of the found value of R is not 
favourable to this supposition. 

A similar calculation is possible for the ratio of specific heats. Assuming the gas 
to contain 5 per cent, of molecules of A 3 , and 95 per cent, of molecules of A x the 
value of y, the ratio of specific heats, would be 1*648. All that can be said on this 
point is, that the found ratio approximates to this number ; but whether the results 
are to be trusted to indicate a unit in the second decimal appears to me doubtful. 

The question must therefore for the present remain open. 


April 9. 

It appears worth while to chronicle an experiment of which an accident prevented 
the completion. It may be legitimately asked, Does magnesium not absorb any 
argon, or any part of what we term argon ? To decide this question, about 
500 grms. of magnesium nitride, mixed with metallic magnesium which had 
remained unacted on, during extraction of nitrogen from ".air-nitrogen," was placed 
in a flask, to which a reservoir full of dilute hydrochloric acid was connected. The 


flask was coupled with a tube full of red-hot copper oxide, intended to oxidise the 
hydrogen which would be evolved by the action of the hydrochloric acid on the 
metallic magnesium. To the end of the copper-oxide tube a gas-holder was attached, 
so as to collect any evolved gas ; and the system was attached to a vacuum-pump, in 
order to exhaust the apparatus before commencing the experiment, as well as to 
collect all gas which should be evolved, and remain in the flask. 

On admitting hydrochloric acid to the flask of magnesium nitride a violent 
reaction took place, and fumes of ammonium chloride passed into the tube of copper 
oxide. These gave, of course, free nitrogen. This had not been foreseen ; it would 
have been well to retain these fumes by plugs of glass- wool, The result of the 
experiment was that about 200 cub. centime, of gas were collected. After sparking 
with oxygen in presence of caustic soda, the volume was reduced to 3 cub. centims. 
of a gas which appeared to be argcn 

mdcccxcv, — A, 2 i